The saddest thing about Wolfgang Amadeus Mozart is the fact that his 235th birthday (which is today) occurs in the same year as the 200th anniversary of his death (next Dec. 5). The most exhilarating thing about Mozart is that during his 35 years 10 months and 8 days on earth, he produced operas and symphonies, quartets and sonatas, masses and songs and curious little works for mechanical instruments and even for tuned water glasses, at incredible levels of quality and quantity.

Somebody has estimated that it would take a professional copyist 12 years to write down all the music Mozart composed in that short life (more than 800 pieces), and that sounds reasonable to me. A lot less time is needed to play a note than to put it down on paper, but Lincoln Center and the various musicians who play there will need 19 months (with ample time off, to be sure) to perform every note Mozart ever composed, beginning with a two-hour birthday gala to be televised today ("Live From Lincoln Center," 3 p.m., Channel 26).

Philips Records, which has begun work on a complete set of Mozart's music, combining new recordings with reissues, expects it to take approximately 180 compact discs, each of which can hold up to an hour and a quarter of music.

Other anniversary projects are less ambitious than these complete surveys, but nearly every musical organization you can name, except those that specialize in the Middle Ages or the 20th century, has a Mozart project in the works. PBS has already telecast two of the three Mozart operas with librettos by Lorenzo da Ponte in the enfant terrible productions of Peter Sellars: "The Marriage of Figaro" (set in the Trump Tower) in December and "Don Giovanni" (set in the South Bronx) earlier this month. Still to come, next month, is "Cosi Fan Tutte." There also will be live productions of "Cosi" by the Prince George's Opera in June and the Summer Opera Theatre in July. Washington has already seen two "Magic Flute" productions in the past year, one at Wolf Trap and another, by the Washington Opera, that has just ended its run in the Eisenhower Theater. Rumor has it that the Washington Opera also will present a "Don Giovanni" before the Mozart year is over, but that has not been officially announced.

The National Symphony Orchestra will present two solid weeks of Mozart programming from March 21 through April 2, neatly balancing the familiar (the "Jupiter" Symphony and the Clarinet Concerto) with the less familiar (the "Idomeneo" Overture and ballet music; Horn Concertos Nos. 1 and 2; the "Impresario" Overture; the "Great" Mass in C Minor). The guest conductor will be Richard Hickox, whose recordings with the City of London Sinfonia have made a good impression in recent years, with hornist Hermann Baumann, clarinetist Richard Stoltzman and the Washington Bach Chorus among the guest artists.

The Friday Morning Music Club Orchestra, which does not have the bottom-line imperatives that face professional orchestras, is well along in a complete survey of Mozart's symphonies, played in various local churches and occasionally in the Terrace Theater.

The anniversary year's most lavish feast of Mozart opera will be presented by the Bravo cable network, which regularly shows a lot more opera and ballet than PBS. On eight Wednesday evenings scattered through the year, beginning with "The Marriage of Figaro" on Feb. 20, Bravo will present Mozart's eight most important operas (including "Cosi," "Don Giovanni," "La Clemenza di Tito," "The Magic Flute," "The Abduction From the Seraglio" "Idomeneo" and "La Finta Giardiniera") in performances from the court theater of Drottningholm in Sweden, a small opera house that has been preserved unchanged (even in its sets and backstage machinery) since the time of Mozart. These historic-instrument performances, conducted by Arnold Oestman, have been acquiring a substantial reputation in the past few years.

The Mozart projects with the deepest and most durable impact are likely to be the recordings. I can recall, when I began collecting records 40 years ago, buying a copy of the Koechel catalogue of Mozart's works, studying it, checking off each acquisition and wondering whether it would ever be possible to collect everything he wrote. Not only can you do that now; you can get two or three different recordings of such rarities as the Adagio in C for Glass Harmonica. Somehow, now that it is possible, it seems less important to have every note he wrote sitting on the shelf. But for those who want it, it is there, and no composer in history is more clearly worth recording and collecting in his entirety.

Two basic decisions face a Mozart collector: whether to buy packaged sets (for example, all the piano sonatas played by Anthony Newman on Newport Classic or by Mitsuko Uchida on Philips) or to shop around (maybe one disc by Newman, another by Uchida, a third by Alfred Brendel). The second is whether to get Mozart on modern instruments (such as Brendel's golden-toned Boesendorfer) or on historic instruments (for example, Newman's 1790 and 1803 fortepianos). Historic Instruments

There are no "right" or "wrong" answers to these questions, only personal preferences, and I can do little more than outline some of the factors relevant to your personal choice.

Newman also conducts Mozart on period instruments on a Newport Classic disc titled "Mozart: Complete Music for String Orchestra," which contains "Eine Kleine Nachtmusik," the three Salzburg divertimenti, K. 136-138, and the magnificent Adagio and Fugue in C Minor, K. 546. This disc has won a special place in my affection precisely because of its eccentricities -- some breakneck tempos and the use of a fortepiano to reinforce the bass line, enrich the harmonies, toss in an occasional little cadenza and sometimes make Mozart sound like Bach. This is like no other Mozart disc on the market, and adventurous listeners should hear it.

Ton Koopman and the Amsterdam Baroque Orchestra give the three early divertimenti a brisk, bright and pleasantly quirky performance on an Erato CD, together with the larger-scaled Divertimento, K. 251. This is party music and treated in that spirit. So is the hour-long Serenade, K. 203, performed on historic instruments by the Collegium Aureum on the Deutsche Harmonia Mundi label. On Teldec, Nikolaus Harnoncourt leads his Concentus Musicus in an "Eine Kleine Nachtmusik" that might sound mildly eccentric to anyone who had not heard Newman's, together with delightful performances of the witty Divertimento, K. 251, and the "Musical Joke."

Historic-instrument recordings of Mozart's symphonies are not as abundant as you might expect, probably because Christopher Hogwood and the Academy of Ancient Music got in so early (on Oiseau-Lyre) with a complete set in outstanding performances. But a few discs deserve special mention. On Philips, John Eliot Gardiner and the English Baroque Soloists have sampled the later symphonies in several discs of outstanding quality, and on Nimbus, conductor Roy Goodman and the Hanover Band have put some of Mozart's greatest hits on two discs: the "Jupiter" Symphony, the Piano Concerto No. 20 in D Minor and the "Serenata Notturna" (NI 5259) and the Symphony No. 40, Clarinet Concerto and a "Kleine Nachtmusik" (NI 5228) much less radical than Newman's or Harnoncourt's. Of the two, I prefer the first collection.

In Teldec's "Das Alte Werk" series Harnoncourt conducts two of Mozart's earliest masterpieces: the Mass in C Minor, K. 139, whichhas the curious nickname of "Orphanage" ("Waisenhausmesse") and the brilliant "Exsultate, Jubilate," K. 165, with its soaring "Alleluia" beloved of virtuoso sopranos. Barbara Bonney is such a soprano, and she finds in this music all the joy and reverence that Mozart put there. His much later Mass in C Minor, K. 427, also has been recorded on historic instruments by Oiseau-Lyre, with Hogwood conducting the Academy of Ancient Music in a well-styled interpretation and Arleen Auger heading a distinguished group of soloists. The two discs, heard together, point up striking contrasts between the incredibly talented teenage composer and the deeper artist in his twenties.

The monumental "Solemn Vespers of a Confessor," K. 339, get an excellent performance from Banchetto Musicale, a Boston-based ensemble, on a Harmonia Mundi disc that also has the Mass in C, K. 317. Two early-instrument recordings of Mozart's "Requiem" also deserve mention. Koopman gives the music high impact in an Erato recording with the Amsterdam Baroque Orchestra, chorus and soloists. Goodman and the Hanover Band and Chorus, on Nimbus, have the first recording of the new edition by H.C. Robbins Landon, who provides informative notes. Three of Goodman's soloists make a better impression than their Erato counterparts: soprano Gundula Janowitz, tenor Martyn Hill and mezzo Julia Bernheimer, who will be remembered from her 1987 and 1989 appearances at the Schubert, Schubert and Schubert Festival. Modern Instruments The big name in modern-instrument recordings of Mozart this year is Sir Neville Marriner, thanks to the Philips "Complete Mozart Edition," which has put him in charge of vast territories, including more than 50 symphonies (divided into two volumes of six CDs each); the orchestral serenades (Volume 3, seven CDs) and the divertimenti for strings and winds (Volume 4, five CDs) as well as several operas. The opera recordings I have heard ("Cosi Fan Tutte" and "The Magic Flute") are new and very good, with all-star casts. The orchestral performances were recorded from 1972 to 1990, but it would be hard, simply listening, to tell old and new apart. All have the crisp precision, careful balance and subtle tonal colorations that have long been hallmarks of Marriner and his Academy of St. Martin-in-the-Fields. Marriner's sense of style is impressive, as usual, and this set can be recommended to anyone who wants all of Mozart's orchestral music played on modern instruments.

Competing performances are many and excellent, particularly for those who do not want complete sets, even if we consider only those that are conducted by people called "Sir." On Telarc, Sir Charles Mackerras and the Prague Chamber Orchestra match Marriner's musical quality in a series that began with the late symphonies and is slowly moving backward toward the juvenilia. The latest installment has Symphonies No. 14 through 18, in performances and sound that should satisfy anyone. Philips gives itself some serious competition in Mozart recordings by the Staatskapelle Dresden, Sir Colin Davis conducting. One CD (Philips 426 236-2) has 1981 recordings of Symphonies 28 and 29, plus a recent recording of No. 34; another (Philips 416 155-2) has recent recordings of Nos. 35 and 38. The sound and performances are both robust, suggesting a larger orchestra than Marriner's. Also well worth hearing (on the Virgin Classics label) are two CDs of Mozart's last (and best) symphonies, Nos. 38-41, with Sir Yehudi Menuhin conducting the Sinfonia Varsovia. Also on Virgin Classics, Menuhin leads the Lausanne Chamber Orchestra in a delectable selection of Mozart's party music.

Still, for those who want the last word on Mozart's orchestral music on CD, Marriner is it for the foreseeable future. His recording is greatly enhanced, by the way, with notes by Neil Zaslaw, whose book "The Mozart Symphonies," published last year by Oxford, is the definitive study.