For me, dreams are mostly entertainment - safe, cheap, available. But for the poet Keats, dreams could be ''more serene than Cordelia's countenance, more full of visions than a high romance.'' For Shelley they amounted to ''thought's wilderness,'' and for Wordsworth they brought ''a substantial dread . . . conjured up from tragic fictions.''

For Shakespeare, the dream state was sometimes a scary pricker of the conscience. In his most famous ''dream'' passage, from Hamlet's soliloquy, he likens it to a guilt-ridden afterlife: To die, to sleep; To sleep: perchance to dream: ay, there's the rub: For in that sleep of death what dreams may come When we have shuffled off this mortal coil, Must give us pause."

At other times, though, the dream for Shakespeare was a blissful retreat. In the six lines that close his Sonnet XLIII, he measures reality against reverie and opts for the latter: How would I say, mine eyes be blessed made By looking on thee in the living day, When in dead night thy fair imperfect shade Through heavy sleep on sightless eyes doth stay! All days are nights to see till I see thee, And nights bright days when dreams do show thee me."

Dreams, in other, more prosaic words, can be all sorts of things.

Benjamin Britten thought so. Dreams, in fact, were one of the composer's preoccupations throughout his adult life, and probably never more on his mind than in the 1950s and '60s. Like dreams themselves, the limits of Britten's ''dream'' period are vague, but it seems useful to mark them with the operas ''The Turn of the Screw'' and ''Owen Wingrave.''

The one dates from 1954, the other from 1970, and neither is about dreams per se. But both operas shed light on the cloudier regions of the human psyche, on the mysterious shadow-world where natural mixes unpredictably with supernatural. ''The Turn of the Screw'' and ''Owen Wingrave'' are the only operas that Britten based on the fiction of Henry James; simply put, they are operatic ghost stories.

Between these two blood-chillers, Britten produced a great many works. Among the lesser-known are the 1954 ''Canticle III: Still Falls the Rain,'' the 1957 ''Songs From the Chinese,'' a 1958 cycle of songs on poetry by Friedrich Hoelderlin, the 1958 ''Nocturne,'' the 1965 ''Songs and Proverbs of William Blake,'' a 1965 cycle of songs after Pushkin and the three one-act operas - ''Curlew River'' from 1964, ''The Burning Fiery Furnace'' from 1966, ''The Prodigal Son'' from 1968 - that Britten called ''church parables.'' The most familiar piece is the 1961 ''War Requiem,'' but a close second is the largely comic opera Britten made in 1960 of Shakespeare's ''A Midsummer Night's Dream.''

On the surface, the ghost stories and the church parables and the song cycles and the rest would seem to have little in common. Yet the texts of all of them - sooner or later, in one way or another - grasp at the same vapory subject matter. They deal with the search for truth - and with the peace of mind that ultimately results from the finding of it. References to death appear often in these texts, for Britten trusted that there would indeed be a truth-based peace in death. But just as often there are references to sleep. The imagery is sometimes intertwined, and one suspects that Britten - like Shakespeare, and like Raymond Chandler - believed death to be a kind of Big Sleep.

Most of the ''sleep'' passages that Britten chose to set, however, are focused clearly enough on sleep of the sort that had actually been experienced by Britten and his various poets. It is a sleep that comes naturally, a sleep that - restful or troubled - is almost always accompanied by dreams.

One of the best sources of information on Britten's attitude toward dreams is his song cycle ''Nocturne.'' Except for the lines from ''Hamlet,'' all the quotations that came early in this article are from the poems that make up Britten's text; along with Shakespeare, Shelley, Keats and Wordsworth, the contributors are Tennyson, Middleton and Wilfred Owen. As specifically as fine poetry can be, all these poems are about dreaming. The music, too, is about dreaming, not about what dreaming feels like but about the truths - for better or worse - that dreaming can uncover.

In his liner-note essay for an Academy Sound & Vision recording of ''Nocturne,'' Paul Riley tells us that Britten was fascinated by ''the duality of night as both dream and nightmare, as magic healer and begetter of terror.'' Riley also notes that the final song - an ominously beautiful setting of the Shakespeare sonnet - ''explores a crucial paradox central to Britten's work: that 'reality' is more properly apprehended by the subconscious than by the conscious mind.''

This is worth considering by anyone who plans to attend Opera Theatre of St. Louis' upcoming production of ''A Midsummer Night's Dream.'' The opera, after all, was completed just two years after ''Nocturne.'' Whatever Britten was thinking as he finished the songs was still going through his mind as he began, in October of 1959, to condense Shakespeare's five-act script into a workable three-act libretto. And it is likely that thoughts of sleep nagged him more persistently than usual; for most of that winter, Britten was sick with the flu.

Ill or not, Britten came through with an opera that is charming from first note to last. The plot needs no summary here, for it closely parallels Shakespeare's. And the score, from a purely theatrical point of view, is self-explanatory; the opera-goer will hear instantly that the ''mechanicals'' are described by clunking rhythms for brass and bassoon, that the lovers are characterized by soft paddings of strings and the upper woodwinds, that Oberon and the other fairies are identified by sparkly figures for percussion, harp, harpsichord and celesta.

The score is self-explanatory, but listeners might want to pay special attention to the music of Act II. Better, they might want to ponder the music - its essence, at least - in advance of the performance. While the whole of the opera can be interpreted as one magnificent dream, the only significant dreaming that takes place on stage begins halfway through this second act. But the harmonies that constitute Britten's ''dream music'' are heard earlier, as the curtain goes up; they permeate the scene, and if one puts them under an analytical magnifying glass, it can be shown that they permeate the entire opera.

They are simple harmonies, playable by anyone within reach of a piano. First comes the chord known as D-flat major, made up of the notes D-flat, F and A-flat. Then, in a higher octave, comes a chord that can be identified either as B minor 7, in first inversion, or D major 6; the notes, in any case, are D, F-sharp, A and B. Then, spread high and low over the pitch range, are the notes (E-flat, G and B-flat) that make up the E-flat major chord. Finally, in the high register, come the two notes C and E.

Eric Walter White, in his 1983 book on Britten's operas, says that this series of four chords typifies ''the drowsy effects of Oberon's magic spell.'' I prefer the assessment offered by Wilfrid Mellers in a chapter he contributed to the 1984 anthology ''The Britten Companion.'' ''Act II deals with the effects of the spell on mortals and immortals,'' Mellers writes, ''and Britten devises for it another exquisitely precise musical image. Four concordant but unrelated chords embrace every note of the chromatic scale and so, like the original forest murmurs, may be said to embrace a cosmos - that of the psyche in sleep.'' Play the chords, slowly, and then repeat them a few times; you'll hear what he means.

Mellers' chapter, incidentally, is called ''The Truth of the 'Dream'.'' It concentrates on the dramatic and musical truth of this particular opera that has the word ''Dream'' in its title. In passing, though, it touches on a topic much broader.

''It is too simple to say that in 'growing up' we are entering reality and leaving illusion behind,'' Mellers proposes in his introduction. ''Our unconscious motivations may be truer than conscious truth, and only in dreams may we be born again. . . . Whatever 'reality' may be, it is not totally contained within . . . social conventions and moral proprieties.'' 

The one pertinent to the first of the four productions - Benjamin Britten's ''Peter Grimes'' - takes the form of an interview with director Colin Graham. That it will not be available to the general public in advance of opening night is unfortunate, for it deserves to be read at leisure, without the distractions of a milling crowd and an orchestra's noisy warm-up routine.

Even persons not yet familiar with the plot and music of ''Peter Grimes'' will find the interview stimulating; it deals with the opera's ''real subject,'' something that has triggered debate ever since the work had its first performance in 1945. Like most serious-minded directors who confront a weighty but still controversial masterpiece, Graham has pondered the question of the ''real subject'' and come up with an answer to which he is - at least for the moment - fully committed. But his comments respectfully illuminate other possible answers.

Graham notes that over the years - between the premiere and his death in 1976 - the composer himself seemed to change his mind about the opera's dramatic essence. Similarly, Graham's own ideas about ''Peter Grimes'' have shifted. If the staging is successful, the audience on Saturday will get a clear enough picture of Graham's new interpretation. But the picture will doubtless be enhanced if the audience is aware as well of the more traditional reading.

The opera has a title character, one prominently featured in all three acts, and so at first glance it would seem that the ''real subject'' of ''Peter Grimes'' is Grimes himself. He is, indeed, a fascinating character, one of the opera world's great anti-heroes, a rough yet philosophical fisherman who is definitely a misfit in his community, arguably a sociopath but nonetheless a man whose villainy is more apparent than actual. And he is a victim, more of circumstance than anything else. The opera begins with an inquest into the death of Grimes' apprentice; even though the death is deemed an accident, Grimes is suspected of foul play. When a second apprentice dies - also accidentally, in full view of the audience - the villagers in effect convict Grimes of murder. His protests of innocence fall on deaf ears. Hounded by accusations and eventually by a mob, he escapes into suicide.

Britten and his librettist, Montagu Slater, based their protagonist on one of the many residents of an English village called Aldeburgh that was colorfully limned by George Crabbe in a lengthy set of poems from 1810 collectively titled ''The Borough.'' It is likely that the character of Grimes had a real-life model, a fisherman named Tom Brown who was a ne'er-do-well around Aldeburgh in the middle of the 18th century. Crabbe's Grimes, in any case, was a quite thoroughly despicable sort who, after being ostracized by the village, spent his last years sailing up and down the nearby River Alde in a state of haunted madness. Britten and Slater altered him considerably not just by bringing him to a more conclusive end but by giving him a conscience and other redeeming qualities.In the opera, Grimes is a vulnerable figure, even a romantic figure. Yet his death results from his own stubbornness, and thus its tragedy has a very classical ring to it.

''Peter Grimes'' is, of course, about Peter Grimes. But the ''real subject'' of the opera seems to be something larger than the events of one man's life. To judge from the profundity of the music and the inexorable momentum with which the drama unfolds, Britten is clearly dealing here with an entity - a force - that is as ominous as it is permanent. Is that force the sea, which constantly batters the town while at the same time providing it with its livelihood? Or is that force the community in which Grimes, as a nonconformist, finds it impossible to survive?

There is no question that the sea looms large in ''Peter Grimes.'' Britten was born in 1913 in Suffolk, the English county east of London that edges on the North Sea. His parents' home was close to the water. According to Imogen Holst's biography, his ''winter days and nights were filled with the buffeting of the cold north-east wind and the sound of the huge waves breaking on the pebbles and the distant squawking and screeches of the herring-gulls swooping and circling above the fishing-boats.''

Britten took his schooling at the Royal College of Music in London. After graduating he remained in the city, participating as much as he could in its musical whirl and supporting himself by producing scores for documentary films put out by the General Post Office. But he kept in touch with the sea. In 1937, after his music had begun to meet with international success, he established residence in a rehabbed windmill near the Suffolk coast. It was just a few miles from Aldeburgh, and it must have pained him to leave it when, in 1939, he moved to the United States.

His exile was self-imposed. As a conscientious objector, he might well have stayed in England during the World War II years. But at this stage of his life he needed anonymity as well as relative peace and quiet. ''In England today the artist feels essentially lonely, twisted in dying roots, always in opposition to a group,'' he wrote in a letter to Louis MacNeice.

The American soil, which had no dying roots, proved fertile for Britten; among the works he produced in this country were the ''Violin Concerto in D Major,'' the ''Diversions'' for piano and orchestra, the song cycle ''Les Illuminations,'' the ''Sinfonia da Requiem'' and the opera ''Paul Bunyan.'' But here, too, he felt ''essentially lonely,'' and on top of that he was homesick. Britten was in California in the summer of 1941 when he came across an article by E.M. Forster in the BBC's weekly magazine.

It was an essay on Crabbe's ''The Borough,'' poetry that Britten had not previously encountered, and the quoted descriptions of the Aldeburgh coastline proved almost more than he could bear. As fine a body of water as it is, the Pacific Ocean, Britten knew, was not the same as his beloved North Sea. War or no war, he resolved to go back to England as soon as possible. He made the return voyage in March of 1942, on a Swedish cargo vessel. Along with a limited amount of baggage, he carried with him a check for $1,000 from the recently founded Koussevitzky Music Foundation and the seedling idea for his second opera.

Supported by the Koussevitzky grant, the opera was to be an adaptation of the ''Peter Grimes'' sections of Crabbe's poem. Britten busied himself with other projects - mostly vocal pieces - during the 18 months it took Slater to construct the libretto. Work on the opera's score began in January of 1944, and it continued without interruption until February of the next year. Crabbe's portraits of the sea at Aldeburgh in part inspired Britten to create ''Peter Grimes,'' and for many listeners it is Britten's musical portraits of that same sea that form the opera's essence.

''It is only rarely that places become the heroes of operas,'' writes Peter Porter in his essay for the English National Opera's volume on this work, ''yet such is the case of 'Peter Grimes.' The opera is first and foremost an evocation of genius loci, and subsequently a gallery of types and humors.''

Another British critic - Christopher Palmer, in a 1984 essay titled ''Chaos and Cosmos in 'Peter Grimes' '' - hedges only slightly when he says that ''the sea is arguably the major protagonist'' here. His account of the opera's famous ''Sea Interludes'' is, indeed, an account of the opera's entire drama. Certainly the gist of it - the premise, the conflict, the resolution - is contained in the seascapes; all that is missing, and some feel that this is insignificant, is the human detail.

Most productions of the opera have taken this view, that the sea is its ''real subject.'' Since Britten's death, however, more and more directors are regarding the sea as simply a metaphor for human society.

Like the sea, society is merciless and unyielding; it is something the individual must confront daily, and it is something that threatens always to swallow up the individual who too proudly resists it. Colin Graham's upcoming production for Opera Theatre will emphasize the work's sociological aspect. At the same time, it will not neglect Britten's potent sea imagery. I'm not sure what Graham has in mind for the ''Sea Interludes'' that play during the scene changes, but his program note hints that they will involve the chorus - the members of the Aldeburgh society - in a significant, apparently unique way.

''The 'Interludes' are not just 'sea pictures' or a sort of weather report,'' he says. ''They're studies of the states of mind of both Peter himself and the people of the Borough. I very much want to bring out the conflicts between the two, and the ambivalence of the crowd and the sea, and to use the conflict to help with the problem of the scene changes. Using the chorus as the sea and as the crowd should show them both as enemies; I've never seen a production which relates one to the other.''

The staging of the ''Sea Interludes'' might be new, but not the idea that the sea and the crowd are somehow related. Graham, who knew Britten well, suggests that the composer probably had this in mind from the outset. He quotes the program note for the 1945 premiere, in which Britten wrote that the opera was at least to a certain extent about ''the perpetual struggle of men and women whose livelihood depends on the sea.'' Then he cites an interview Britten gave on the occasion of the work's first performance, in 1948, by the Metropolitan Opera; what it's about, Britten said, is ''a subject very close to my heart - the struggle of the individual against the masses.''

The easy answer to this introspective query is that the savior is Billy Budd, the handsome and personable sailor whose name serves as title for the 1951 work by Benjamin Britten that Opera Theatre of St. Louis will offer Thursday, next Saturday and June 16, 18 and 20 as the final production of its current season. But the question is a good one, and it lingers after the conscience-stirring opera has sailed its course.

Captain Vere's opening soliloquy is voiced from the perspective of an old man looking back on a long life marked as much by successful seafaring as by unsuccessful grappling with weighty moral issues. The bulk of the opera is told in flashback, but it returns to "real time" for the epilogue. Once again the key verb is heard. This time, however, its object is not the captain but Billy. "We committed his body to the deep," Vere remembers. "The sea-fowl enshadowed him with their wings, their harsh cries were his requiem. ... I could have saved him. I could have saved him. He knew it, even his shipmates knew it, though earthly laws silenced them."

Earthly laws silenced the captain, too. He was the only witness to Billy's killing of a man. But he was also the commanding officer of a ship in the British navy. The captain was aware that the killing was more accidental than deliberate, and that Billy - long hounded by the ship's master-at-arms and unjustly accused by him of mutinous sentiments - had good reason to lash out. At the trial, Billy explained that he hit the master-at-arms with his fist only because his severe stammer prevented him from defending himself with words. "Captain Vere, save me," Billy pleaded just before the verdict was reached. But an explanation from the captain would have done no good. Under any circumstances, the killing of an officer by a seaman amounted to a capital crime. Justice, the captain knew, had to be served. In spite of what he says in the opera's epilogue, it is not likely that the captain could have saved Billy.

Just how it was that Billy managed to save the captain is, at the very least, unclear. What is not in doubt is that Britten's "Billy Budd" - to a much greater extent than the Herman Melville novel on which it is based - centers on the idea of redemption. "Salvation at Sea" is the subtitle musicologist Philip Brett attached to the essay on "Billy Budd" he contributed to a valuable 1984 collection of essays on Britten. For Andrew Porter's 1978 review of several "Billy Budd" productions, the editors at The New Yorker magazine used as a headline the single word "Saved." Referring to his contribution to "Billy Budd," librettist E.M. Forster noted that his valedictory short-story about two men who destroy each other was "more interesting than the theme of salvation, the rescuer from 'otherwhere.' " In the opera, Billy's last words - before he ascends to heaven at the end of a hangman's rope - are "Starry Vere, God bless you." It is a calm benediction, and its straightforwardness hints that it is indeed Billy who somehow from "otherwhere" rescues the captain's tormented soul.

Colin Graham's staging of "Billy Budd" for OTSL will perhaps hold to the norm and depict a spiritual rescuing of one sort or another. In any case, the final paragraph of Graham's synopsis informs us that the captain - "haunted" by Billy's blessing "all his life" - "at last. . . finds resolution." Curiously, though, the opera does not end on a peaceful note.

There is musical resolution here, but its effect is short-lived, and much more noticeable at the start of the epilogue than at the end. The execution scene devolves quickly into a storm of bone-chilling dissonance, and then just as quickly the harmony settles; the chords of B minor and B-flat major that press so gratingly against each other during the captain's first soliloquy are, at the start of onset of his last speech, reduced to a conclusive enough triad on B-flat. The rolling rhythms that early in the opera seem to depict troubled waters, however, are still very much to be heard. Most of the captain's speech is punctuated by sharp blows on the timpani that suggest ominous thunderclaps. The very last words are half-sung, half-spoken with no instrumental support at all; they come slowly, and they drift downward, as into an abyss.

In the article on "Billy Budd" he wrote for The New Grove Dictionary of Opera, Britten scholar Arnold Whittall offers a provocative reading of the opera's final gesture: "As (the B-flat major chord) dies away, Vere sings again the words that ended the prologue, to a vocal line whose descending pitches cast a shadow over the serenity of the harmonic resolution. Whether he has truly found peace, or whether he is doomed endlessly to relive the most powerful and traumatic event of his life, unable to find release even in death, is a question the opera leaves open."

The epilogue ends darkly, with sounds that suggest not so much redemption as damnation. The listener who thinks back to the end of the trial scene, however, might be able to make sense of the apparent contradictions. Billy is not in the courtroom when the verdict is announced. Captain Vere hears it and accepts it. He sings an aria during which he describes himself as the destroyer of "beauty, handsomeness, goodness." Then he goes to Billy's cell to inform him of the death sentence.

"The opera makes its deepest statements through harmony," Andrew Porter wrote of "Billy Budd." Probably nowhere is Britten's statement more profound than in the sequence of chords that follows the captain's aria. There are 34 chords in all, each one different in sonority as well as in pitch content, yet somehow related to the notes that make up a simple F major triad. A few of them will be heard again in the next scene, when Billy sings "I'm strong, and I know it, and I'll stay strong, and that's all, and that's enough." The first time around, they speak not just of strength but of serenity. Porter called them "mystical, sacramental." For Britten biographer Eric Walter White, they sound like "a rainbow of hope."

There are many powerful episodes in the "Billy Budd" score, but none seems so potent as this quiet orchestral interlude. Elsewhere, salvation is only talked about; here, when words are abandoned, salvation is actually depicted. In an opera rich in ugliness and violence, this is a moment of incontrovertible beauty. In an opera laden with lies and self-deceptions, this is a rare moment of truth. Yet the questions remain: Who is the savior? Who is saved? Why is he saved? What is he saved from?