His not quite unequivocal rejection of the very idea of opera on film was prompted by Jean-Marie Straub's then new version of Schoenberg's ''Moses und Aron.'' Simon was not fond of ''Moses und Aron'' in the first place. Straub's film, he wrote, only exaggerated its ''lifeless, biblico-metaphysical maundering,'' and the photography - mostly ''closeups from often unlikely angles or, contrariwise, very ordinary long shots and excessive circular pans'' of a ''pseudoperformance'' of the opera in ''an empty, semiruined amphitheater'' - amounted to the ultimate in cinematic dullness.

Simon's damnation of the Straub film stirred up little controversy. Most people who saw ''Moses und Aron'' agreed that, as far as movies go, it was lousy.

But Simon's negative appraisal of another opera film just a month later bothered many of his readers.

Movie fans as well as operaphiles generally regarded Ingmar Bergman's 1975 treatment of Mozart's ''The Magic Flute'' as a breakthrough, a lightweight and charming yet distinctly Bergmanesque interpretation of the work that respectfully - some would say ingeniously - met the needs of both opera and film.

Simon granted that this was probably ''the best filmed opera ever,'' and he went on to laud Bergman for his choice of cast, his cinematography, his editing and his decision to ''set'' the opera not in its own fictional time but in the present.

All the compliments, though, were backhanded. As intriguing as Bergman's ''Magic Flute'' is, Simon wrote, it only proves the point that ''opera on film is an impossibility.'' ''The trouble with putting opera on film,'' he summarized, ''is that even when you do it right, you are wrong to do it at all; you are only reminding us how much better the thing is in the opera house, where it belongs.''

Is opera on film an impossibility?

The question comes up because Franco Zeffirelli's latest opus - a film version of Verdi's ''Otello'' starring Placido Domingo, Katia Ricciarelli and Justino Diaz - is showing this week at the Tivoli Theatre in University City.

Like the other opera films that have visited commercial movie houses since Bergman's ''Magic Flute,'' Zeffirelli's ''Otello'' is something conceived specifically for the wide screen. Bergman's ''Flute,'' it should be noted, was originally made for television; it was shot mostly inside Sweden's intimate 18th-century Drottningholm Theatre, with the actors, in effect, playing the parts of artists appearing in a modern but nonetheless old-fashioned staging of the opera.

''Otello,'' in contrast, follows the tradition of Joseph Losey's 1979 ''Don Giovanni,'' Francesco Rosi's 1984 ''Carmen'' and Zeffirelli's own 1983 ''La Traviata.'' As in most movies, the acting and the settings are entirely realistic. The imagery is constantly enlivened by zooms, dissolves and quick cuts; the screenplay makes generous use of such uniquely cinematic narrative devices as montage and flashback.

Opera purists doubtless will object to Zeffirelli's ''Otello.'' The excisions total about 30 minutes, roughly one fifth of the opera's normal running time; along with many bits of dialogue, the deleted sections include such worthy episodes as Iago's duet with Cassio in Act III, the big ensemble number at the end of the same act and Desdemona's ''Willow Song'' in Act IV. There are insertions as well as cuts; a wedding scene, propelled by jangly ballet music that Verdi wrote for the third act of an 1896 Paris production of ''Otello,'' pops up in the middle of Act I, for example. And at the film's end, Zeffirelli replaces Verdi's brief but conclusive coda with a five-minute postlude based on music that earlier accompanied the title character's fateful entrance into his wife's bedchamber.

The opening credits do inform the viewer that Arrigo Boito's libretto has been ''adapted'' for this film by Zeffirelli and one of his assistants; the credits fail to mention how much of the libretto has been altered, not by changing the words but simply by leaving out a lot of important stuff. Indeed, the omissions are so substantial that purists might argue that this is not a film of Verdi's and Boito's ''Otello'' but a Zeffirelli creation that only uses the opera as its jumping-off point.

Zeffirelli, on the other hand, would argue that his ''Otello'' film is simply an interpretation of an opera he has long known and loved. In an article printed in the Italian magazine Panorama before the film went into production, he discussed in general how he planned to take liberties both with Verdi's music and with Boito's libretto. In his recently published autobiography, he explains the precise motivation for some of his alterations.

Regarding the long flashback sequence that animates the love duet, for example, Zeffirelli suggests that such a treatment is implied by the opera's text. The scene is not found in Shakespeare's play, although the information it contains is scattered throughout Act I of ''Othello''; Verdi and Boito dropped the entire first act of the play when they converted ''Othello'' into ''Otello,'' and they concocted the duet in order to explain the history of the relationship between Desdemona and her husband.

Zeffirelli says that he does visually what Verdi and Boito did musically and literarily; his insertion of the ''wedding music'' and its concomitant festive images, he says, is just a way of expanding on what is already in the script.

As for the scrapping of the ''Willow Song'' in the final act, Zeffirelli says that the song ''delays the action drastically.'' Either it or Desdemona's ''Ave Maria'' had to go if the audience's attention was to be held, he says. Because he wanted to emphasize the religious convictions of all the opera's characters - including Iago - he decided to cut the song and focus on the prayer.

All the changes, Zeffirelli says, are examples of what happens - of what should happen - when a work is translated from one art form into another. He reminds his critics of the many liberties Verdi and Boito took with Shakespeare. He shares the opinion of certain opera scholars that, precisely because they took the liberties they did, Verdi and Boito actually improved on Shakespeare. And he suggests that Verdi ''would hardly object to my humble attempts to improve on him.''

Whatever one makes of Zeffirelli's alleged improvements on Verdi, it remains that his ''Otello'' is a film that - as film - works.

Its failings - the bad lip-synching, the absurdity of seeing Domingo in blackface - were duly noted in Joe Pollack's review in Friday's Post-Dispatch. Also noted were some of the film's many virtues: its uniformly excellent acting, its scenery that is not only spectacular but powerfully evocative of unsettled states of mind, its virtuosic use of cinematic techniques not for the sake of mere effect but for the purpose of amplifying the director's particular interpretation.

These days, Zeffirelli says, he reads ''Otello'' not as a tale of murder provoked by jealous love but as a dramatic conflict in which the protagonist and antagonist are the very essences of good and evil. It's a valid reading. Zeffirelli is committed to it, and doubtless he would strive to realize it were he to direct ''Otello'' in the opera house.

One can easily imagine a staging in which the sets, like those in the film, are symbolic chiaroscuro studies in black and white, in which the character of Iago is presented not as the embodiment of evil but as a frail human being temporarily - albeit absolutely - possessed by evil.

Such a staging, however - even if it were mounted by Zeffirelli - would not have the same impact as that of the film.

Operas and movies have much in common: They occupy finite periods of time, they tell stories, they attempt to engage their audiences with a mixture of music, words and visual images. But the media are different, as different in their potential as they are in their limitations. A Zeffirelli staging of ''Otello'' might be just as powerful as the film; the overall effect, however, could only be similar, not identical.

There is no way that opera on film can provide its audience with exactly the same experiences offered by opera in the opera house. Its performances are ''frozen,'' for one thing, and the points of view - literally - are determined exclusively by the director. If one defines ''opera'' as the sort of theatrical magic that can transpire only in the opera house, then of course opera on film is - as John Simon claims - an impossibility.

But such a definition, I think, is foolishly narrow, especially in this day and age.

I agree with the purists who feel that Zeffirelli's ''Otello,'' because of the severe cutting, does disservice to one of the greatest masterpieces in the 19th-century Italian operatic repertoire. But I also agree with those who feel that Zeffirelli's ''Otello'' is something of a masterpiece in its own right.

When the name of Wagner comes up, invariably the speculation reaches far beyond mere music. A modern Wagner would of course dazzle the world with scores of impressive scope and substance. But the score would be just one element among many in the modern Wagner project. Wagner refined the idea of the Gesamtkunstwerk - the "total art work" - and surely the term would apply to anything a reincarnated Wagner might concoct. As he did in the19th century, Wagner today would write not just the music but the texts for his theatrical pieces; he would direct them himself; he would control the design of their sets and costumes. And it's hard to imagine he would limit himself to the stage. Were Wagner alive today, he would probably be the dictatorial head of a multimedia conglomerate.

It is the "Parsifal" of the real Wagner, not a fictitious one, that will be on TV this week, and it is a version that originated not in a studio but on the stage of the Metropolitan Opera. "Parsifal" tells the tale of the Knights of the Holy Grail, in particular the tale - based on medieval legend - of "an innocent fool made wise by pity." Part of the PBS network's "Great Performances" series, the 41/2-hour telecast is scheduled on Channel 9 beginning at 7 p.m. Wednesday; it will be aired in stereo, with subtitles, and simulcast on radio station KFUO-FM. James Levine is the conductor; the cast features tenor Siegfried Jerusalem in the title role, mezzo-soprano Waltraud Meier as the sorceress Kundry, bass Franz Mazura as the sorcerer Klingsor and bass Kurt Moll and baritone Bernd Weikl as the knights Gurnemanz and Amfortas.

The international stature of the cast notwithstanding, the most significant thing about this "Parsifal" is its staging. It's by Otto Schenk, an Austrian director famous for defending the traditions of Wagnerian opera against the onslaughts of reformists. Like the story itself, Schenk's reading of "Parsifal" is old-fashioned. Still, the production seems very much of our own time. When the opera was on the boards at the Met a year ago, professional critics were struck by its almost "cinematic" quality. On Wednesday night, amateur critics across the country will perhaps marvel at how genuinely "televisionistic" it all looks.

Because viewers will not be watching them flicker simultaneously on a scrim and a stage wall some 60 or 70 feet high, the projections that designer Guenther Schneider-Siemssen uses for the scene changes will not have a three-dimensional feel. Nor will viewers get much in the way of grand vistas. In the theater, Schneider-Siemssen's realizations of the Good Friday meadow and the Monsalvat castle must have seemed vast, indeed. On television, the big pictures are necessarily reduced; they are fragmented into backgrounds for one shot or another, and only rarely - usually at the beginning or end of an act - are they shown whole. That's not to suggest, however, that this "Parsifal" is visually unappealing. The television version seems deliberately to downplay effects that are unique to the opera house. But in their place it offers a full measure of effects unique to the small screen.

The person responsible for these effects is Brian Large, an experienced video director for whom the camera has never been merely an objective observer of operatic action.

Large's cameras take perspectives not available to Met patrons who were sitting in the auditorium on the night of the taping. Indeed, they view the opera in ways that no single pair of human eyes ever could. The cameras are able to zoom in and then fade back, of course. But they can just as deftly circle around a performer or show the profile of an emoting soloist melting into the silhouette of the silent character to whom his lines are addressed. Even when a singer is standing still, the cameras can make him seem to move. And because the video images do move, constantly, they have the potential to be as rhythmic as anything in the score.

While Large's video technique is impressive, his contribution to "Parsifal" goes much further than that. In the opera house, a seductive twinkle in a mezzo-soprano's eye is a detail likely to be noticed only by a person with binoculars who happens to be looking in the right place at the right time. But the cameras, along with focusing their lenses, can focus the audience's attention precisely on that sort of thing. In fact, often there is no room on the television screen for anything but intimate subtleties. The camera work for "Parsifal" teems with nuance, most of which seems relevant to the opera's story line and thoroughly in keeping with Otto Schenk's straightforward approach to the staging.

But surely every Wagnerian worth his salt will find at least something with which to quibble here; all things considered, the morning-after discussions are likely to be very complicated. Keep in mind that, in terms of the drama, this "Parsifal" is the carefully considered work of Schenk. Keep in mind, too, that what the television audience will see is Schenk's vision as filtered through the eyes of Brian Large. And while you're at it, remember that Wagner was the original Gesamtkunstwerkmeister, an authoritarian genius who either created or personally supervised almost every aspect of his operas.

"Parsifal" was Wagner's final opera; it was conceived in 1845 but not completed until 1882, when the composer's control over his "total art work" was most complete. For the purist, a "Parsifal" production requires nothing more than that Wagner's instructions be followed to the letter.

Schenk is certainly a purist, but he is also an opera director. However much he wants to do the master's bidding, it is his job to bring "Parsifal" to life. He can try as hard as he likes to keep himself out of the picture. Still, it falls to him to translate Wagner's 19th-century orders into 20th-century theatrical reality. Brian Large, with his cameras, is likewise a translator, an interpreter. Wednesday night's opera, then, is an interpretation of an interpretation of a "total art work" that arguably needs no interpretation.