Rihm is a 39-year-old composer from West Germany, and his 1987 ''Oedipus'' was given its American premiere earlier this summer by the Santa Fe Opera. It fit into a typical Santa Fe season. Rihm's boldly modernist one-act opera was the almost obligatory new work; the standard repertory items were Mozart's ''The Marriage of Figaro'' and Verdi's ''La Traviata,'' and the two curiosities by popular composers were Puccini's ''La Fanciulla del West'' and Richard Strauss' ''Die schweigsame Frau.'' As is so often the case with Santa Fe's sophisticated but generally conservative audience, attendance for the new piece was slim. Unseasonable rain put a damper on many of the Santa Fe events this month, and the ''Oedipus'' that I witnessed did not escape the showers. But the empty seats at the Aug. 9 performance (the third of four) could hardly be attributed to the weather; the Santa Fe regulars who willingly get soaked in the presence of Mozart or Verdi chose not to buy tickets to this one.

They missed a bracing score loaded with neo-expressionist Angst, an effectively garish but perhaps over-interpreted staging by Francesca Zambello and a credible performance that featured two of the singers (mezzo-soprano Emily Golden as Jocasta and bass-baritone William Dooley as Tiresias) who were members of the original 1987 cast in Berlin. More significant, they missed hearing and seeing a noble attempt at a solution to a very knotty operatic problem.

Myth has always been a troublesome subject for opera. Its distinctive quality is not familiarity but truth, yet its truth is usually ineffable. Fairy tales, parables and legends might be as well-known as myths, but few of them go so far as myth does in explaining - or at least justifying - the complexities of the human condition. Most stories that ''everyone'' knows are clear-cut lessons in morality; myth, because it deals with the mysterious inner workings of the psyche, remains disturbingly open-ended, and therein lies its power. Therein, too, lies the difficulty in its transformation into opera.

When the source of an opera is a novel or a play, the problem faced by the opera librettist involves reduction. For better or worse, the ''Marriage of Figaro'' book that Lorenzo da Ponte fashioned for Mozart is but a digest of the Beaumarchais comedy on which it is based; ditto for Stefan Zweig's text for ''Die scheigsame Frau'' (an adaptation of Ben Jonson's ''Epicoene, or The Silent Woman''), for Francesco Piave's script for ''La Traviata'' (after Alexander Dumas' ''La Dame aux Camelias'') and for Guelfo Civinini's libretto for ''La Fanciulla del West'' (a treatment of David Belasco's play ''The Girl of the Golden West''). Invariably, the original characters do and say much more than do their operatic counterparts. And this is necessary, for opera's extended vocalizations and instrumental interludes make it a relatively slow-moving medium; if a complete story is to be squeezed in before the final curtain falls, the material simply has to be condensed.

When myth is made into opera, on the other hand, the problem involves not compression but expansion. In order for any story to be turned into a viable work for the lyric theater, its characters must be given words to sing and actions to perform. An orchestral tone-poem that purports to tell a story can afford to be vague, and so - to a certain extent - can a ballet. But in opera, mood-setting alone won't do. It is not enough for a hero to express his grief or his joy in abstract terms; the bases of his emotions and the rationale for his behavior must be, somehow, illustrated, and so details of the plot must be made specific.

Myth, in its purist form, does not need such detailing. Its characters are icons, not real people, and the situations into which they are thrust are symbolic of universal human predicaments. For the person who cares to contemplate a myth, it suffices to know only the plot's most basic elements.

It suffices to know, for example, that Orpheus - a favorite of Monteverdi and other of opera's pioneers - was a proud individual who pitted his creative energy against fate and had to suffer the consequences. It is enough to know that Oedipus attained his freedom from childhood only after he resolved his hostility toward his father and his attachment to his mother. That Orpheus was a musician whose beautiful singing swayed the rulers of the underworld to restore life to his dead wife Euridice is not important, in the long run, to anyone's understanding of the myth. Nor does it matter that Oedipus' father was the Theban king Laius and his mother the queen Jocasta, that they abandoned their son at birth because of a horrific prediction by the oracle at Delphi, that Oedipus killed Laius quite by accident and innocently claimed Laius' widow as his wife, that Jocasta committed suicide after realizing the awful truth of her incestuous relationship with Oedipus, that Oedipus blinded himself with Jocasta's brooch and slunk off to a life of bitter solitude at Colonus.

In these and all the other myths that endure, the crucial elements can be boiled down to just a few words; everything else is decoration, layered on by generations of authors so that the germ of the myth - the concept - might be turned into a narrative marketable to a contemporary audience. Embellishments and up-datings are not necessary to myth. They are, however, necessary to storytelling, and often they get in the way of myth's message.

To his credit, Wolfgang Rihm respects the unadornable essence of the cryptic myth he decided to set to music. Unfortunately for his effort, he is not so respectful of the basic requirements of opera.

Rihm's ''Oedipus'' is an 85-minute sequence of 10 vignettes, two of which are pantomimes. The libretto is of the composer's own making, and in its printed form it consists of a mere 26 pages of widely spaced, widely margined lines; although the libretto draws freely from such sources as Sophocles' ''Oedipus Rex,'' Heiner Mueller's ''Oedipus Commentary'' and Nietzsche's ''Oedipus: A Dialogue of the Last Philosopher With Himself,'' it contains little in the way of plot-propelling information. Action, too, is held to a minimum, at least according to the composer's stage directions. There is an assumption here - a safe one, I think - that the audience's foreknowledge of the Oedipus myth is solid and full; except for the two ''flashback'' mime sections and a confrontation scene that involves echo-laden dialogue spoken over a public-address system, Rihm's re-telling of the story is hardly a ''telling'' at all. Rihm's ''Oedipus'' certainly has a text, so it cannot be termed - if such a contradictory term is allowed - a non-verbal opera. Yet that, I think, is what it aspires to be.

The demanding title role at Santa Fe was handled by baritone Rodney Gilfry. Like the others in the cast, he seemed comfortable enough with the English words provided him by translator Carol Borah Palca. But Rihm's vocal lines - angular phrases interrupted by sharp punctuations from brass and percussion, stutters and gasps repeated in insistent rhythmic patterns, soaring flights on sustained vowels - more often than not stripped those words of their normal communicative function. What Rihm's vocal writing did communicate - vividly, chillingly, - was the raw emotions experienced by his characters.

That these emotions are consistently painful doubtless drives home the meaning of the Oedipus myth. At the same time, it makes for an opera that, dramatically, is rather flat. Always pushing as it does toward the extreme edges of discomfort, the score lacks contrast and, as a result, dynamic movement. Rihm's ''Oedipus'' has an eerie feeling of stasis about it. As the lights go up for the lurid depiction of the plague-stricken Thebes, the listener gets the feeling that he is simply tuning in to a woe that has always bothered mankind. As the lights fade on the blind protagonist's halting exit, he gets the feeling that Oedipus will wander forever. Everything that happens in between - the gestures and the words as well as the music - suggests miseries similarly eternal.