MUSIC IN WASHINGTON is mostly Mozart this week, even with a saxophone festival at the University of Maryland and an International Bach Competition at Lisner Auditorium. This year's Mostly Mozart Festival, running through Saturday night at the Kennedy Center, is retailing the hottest classical music property of 1985.

In the year of Bach and Handel (both having 300th anniversaries), the obstreperous young hero of "Amadeus" has elbowed his way into the spotlight with a movie that captured a bundle of Academy Awards. And the Mozart frenzy is likely to continue accelerando and crescendo (with careful orchestration from the music industry) at least until the bicentennial of his death in 1991.

Of all the great classical composers, Mozart is the one whose music is not only admirable but also instantly and spontaneously likable.

On records, Mozart has been a hardy perennial for most of the century. The boom began in the 1930s, spearheaded by a series of opera recordings that originated at the Glyndebourne Festival in England. They emphatically established the proper style for Mozart performance: a classically oriented ensemble style -- light, nimble and beautifully balanced -- contrasting with the high-powered romantic virtuoso approach then favored in the major opera houses. Now, the Glyndebourne Festival is back in the spotlight, bringing Mozart opera to home video.

Just released on the small, enterprising Video Arts International label are video cassettes of Mozart's three top operatic hits: "The Marriage of Figaro" (VAI-OP-6), "Don Giovanni" (VAI-OP-7) and "The Magic Flute" (VAI-OP-5). All three are highly commendable productions. "Figaro" (whose cast includes Kiri Te Kanawa, Frederica von Stade and Ileana Cotrubas, with John Pritchard conducting) is a clear-cut first choice. The operas are issued in Beta hi-fi or VHS and should be available at well-stocked record stores. Or order from Video Arts International, P.O. Box 153, Ansonia Station, New York, NY 10023.

The tapes are of live performances with audiences, originally taped for British television, and they are not completely free of the occasional pinched high note or other random mishap. But all are vintage performances and enjoyment grows with repeated exposure.

The "Don Giovanni" and "Magic Flute" (both superbly conducted by Bernard Haitink) may eventually have significant competition if Joseph Losey's striking (though unevenly reviewed) "Don Giovanni" movie and Ingmar Bergman's eccentric but wonderful "Magic Flute" are released in home-video formats. There have been other television productions (for instance, the playful Salzburg "Magic Flute"), which should eventually find their way to videotape. But the Glyndebourne performances and the VAI processing set a high standard for future issues to match.

The operas are presented with subtitles and without librettos. Those who like to have a book to study might shop around for the full operatic scores of each of these masterpieces, published by Dover Books in excellent, highly readable editions and priced (amazingly) in the $9 to $12 range. Also, this "Don Giovanni" production (directed by Peter Hall and dating from 1977) was the subject of a book containing a day-by-day account of the preparations, interviews with some of the principals and some fine observations on the art of bringing opera to life. "The Making of an Opera: Don Giovanni at Glyndebourne," by John Higgins, was published by Atheneum in 1978.

Listed below are some noteworthy, current sound recordings of Mozart: MOZART:

CHURCH SONATAS -- London Baroque Ensemble (Harmonia Mundi compact disc HMC 901137). These tiny works for organ and strings have been eagerly seized upon by such organists as E. Power Bigs and Carl Weinrich as the only music Mozart composed for the instrument. But most of them are works with organ (to enrich the sound and fill in the harmonies) rather than for organ. This performance, by a finely balanced chamber ensemble playing on original instruments, is a revelation. THE SYMPHONIES:

VOL. 4 -- Symphonies 25, 28, 29, 30; three unnumbered symphonies in D, K. 203, 207a and 213a. The Academy of Ancient Music, Christopher Hogwood (Oiseau- Lyre D170D3, three LPs with booklet). This volume, chosen more or less at random from the complete set, shows Mozart from the age of 17 to 19, leaping from the status of child prodigy to that of a fully mature musician, equal to any composer alive. The 'little' G minor symphony and the Symphony in A are particularly noteworthy and fairly well known. They and the less-known works have both ease and a natural vitality in these performances on original instruments, superbly conducted by Hogwood. EINE KLEINE NACHTMUSIK

Musical Joke; Divertimento in D, K. 136." Academy of St. Martin-in-the-Fields Chamber Ensemble (Philips compact disc 412-269-2). This familiar music receives a new lease on life in these lithe, graceful chamber-music performances with one instrument to a part. The compact- disc sound is a model of clarity.