HAVING MADE one operatic film, director Joseph Losey thinks he will probably want to do others. But there is one small problem. "What can you do for an encore," he was asking himself the other day, "after you've done 'Don Giovanni?"

His movie of the Mozart masterpiece, which many critics and even other composers have called the greatest of all operas, will have its world premiere tonight at the Kennedy Center. It was something new for Losey, who loves Mozart but is not much of an opera fan and still has never seen a staged production of "Don Giovanni." And it is something new in the history of both film and opera -- likely to be the first of many such productions.

Unlike Bergman's "Magic Flute," which was a tentative beginning of the new trend, Losey's "Don Giovanni" includes every note of Mozart's score and every word of Lorenzo da Ponte's libretto. And unlike all the other operatic films made since movies acquired sound, it was produced specially for this medium -- not as a filmed memento of a stage production.

It also is the first operatic film to be produced with a new medium in mind:

the videocassette or video disc, which in a few years may be the standard form of recorded opera in the home. If the recording industry develops as some observers think it will, most well-stocked hi-fi collections by the end of the century will probably have Losey's "Don Giovanni" on a shelf with sight-and-sound recordings of "Carmen," "Tosca," "Il Trovatore" and a dozen others.

The soundtrack was the first part of "Don Giovanni" to be produced. In late June and early July of 1978, in Paris, conductor Lorin Maazel made what amounted to a standard operatic recording (available from Columbia Records) with Ruggero Raimondi, Jose van Dam, Teresa Berganza, Kiri Te Kanawa, Edda Moser and Kenneth Reigel heading a carefully selected cast -- picked not only for their voices but for acting talent and the ability to look like the characters they represent -- even in the demanding detail of a close-up shot. All the cast were veterans in their roles except for Teresa Berganza, who had never sung the part of Zerlina before. Otherwise, the only newcomer to "Don Giovanni" was Losey.

When shooting began in mid-September, a substantial part of Losey's work was a fait accompli: His soundtrack was "in the can" and his cast had been picked by Rolf Liebermann, director of the Paris Opera and the moving spirit be hind the whole production. Losey's assignment was simply to add images synchronized to the sound, using performers who were strangers to him. There also was the question of scheduling. Each of the principals is a jet-age star performing regulary on two or three continents, and their orbits are seldom synchronized.

"We had a hell of a time with schedules, of course," Losey recalls. "Someone was always running off to do one night in Tokyo or one night in Rio. I never had them all together at one time except for the beginning and the end."

Another negative effect of the jet-age star system is the problem of the singer as an interchangeable part. Performing the same role in a variety of productions, often with little or no time to rehearse as part of an ensemble, the jet-set opera star tends to develop an all-purpose interpretation that will fit in with a production in Stockholm or seattle one week, Montreal or Buenos Aires a week later.

"In this situation," says Losey, "they naturally and understandably tend to give superficial performances. They fall back on operatic cliches, which I fought from the beginning. I started this production with the feeling that the usual operatic stage gestures are too large, too sweeping to work on film, and we worked hard at toning them down. Then, as we got to know and trust one another, I found the music carrying me in the other direction, and I was urging them to go farther. As it worked out, the gestures are larger than you usually see on film, but less so than in staged opera -- and not empty, as they are in most operatic productions."

Having a prefabricated soundtrack helped with one problem that crops up constantly when opera encounters the camera: Close-up pictures of a singer hitting a not at high volume are frequently ugly. The face shows signs of the considerable strain involved in lofting a note to the third balcony, and the mouth is twisted far out of shape to accommodate the vowel being produced.

"In the filming, the performers sang their lines again to match a playback of the soundtrack," Losey says, "but they weren't being recorded and they were able to sing at half-voice, as they often do in rehearsals. The result on film is that you can see that they are singing, but they don't have to distory their faces."

Distortion is usually the name of the game when a film is made from an existing work of art. (Ask any novelist who has seen his work on the screen.) In the case of "Don Giovanni," Losey accepted the words and music totally, without change, and seemed to have no problem with this requirement. Asked whether he would hire Lorenzo da Ponte as a script writer if he were available, he says, "I think I would. He is very much underestimated."

But changes were made in translating the opera to film. The scene of the opera is Seville, but in the film it is moved to the Veneto region of Italy, around Venice and Vicenza, so that the striking architectural work of Andrea Palladio (1508-1580) could be used as part of the visual statement. Losey and his associate, Frantz Salieri, also added a non-speaking character, "the valet in black," who is used, Losey explains, "as a kind of observer through whom the audience could be led to see what I saw."

(Salieri, incidentally, is not related to the composer of that name who was one of Mozart's chief rivals and is now nearly forgotten except for one striking detail of his life. After Mozart's death an apocryphal story ran through Vienna that he had been poisoned by Salieri. Long ago rejected by biographers, the story has nevertheless survivied and has even been made the subject of an opera. The modern Frantz Salieri, a Frenchman born Francis Savel, adopted the more resonant name of the composer in the late 1960s for its symbolic overtones.)

Even though he leaves the script unchanged, Losey as director naturally gives the work an interpretation. In a lengthy analysis of Don Giovanni's character which accompanies the Columbia recording, he describes the opera as a very modern piece of work, a drama of social class, and notes that the Don uses sex like a drug, runs away from women of the upper class and pursues women of the servant class. "He is a lost soul, but a privileged lost soul," Losey comments. To express his opinion of the opera, he opens the film with a quotation from Antonio Gramsci, founder of the Italian Communist Party: "The old is dying and the new cannot be born; in this interregnum a great variety of morbid symptoms appears."

Losey's own preoccupation with "morbid symptoms" appeared early in his career, with such pictures as "The Boy With Green Hair," "The Prowler," and a remake of Fritz Lang's classic "M." Then the symptoms began to appear in real life, as red-baiters invaded Hollywood and Losey became one of their targets. In 1954 and 1955, he directed several films under other names, and since then his base of operations has been in Europe.

If "Don Giovanni" is a success, Losey will probably face a difficult choice. More operatic projects will undoubtedly be offered to him -- he expects to begin discussing some possibilities next week -- and he is willing to consider them if something as interesting as "Don Giovanni" comes along. But his real ambition is to make a film of Proust's "Remembrance of Things Past" (more morbid symptoms?) for which he collaborated on a screenplay with Harold Pinter several years ago.

"The screenplay was published here and in Europe," says Losey, "and it did well both in reviews and in sales. If 'Don Giovanni' works as I hope it might, it may open some doors for Proust. The ironic thing is that when we wrote the screenplay, the picture could have been produced for $5 or $6 million. Now, it will cost three or four times that much."