Several musical masterpieces might not be around today had it not been for the intercession of later major composers. For instance, Bach's ''St. Matthew Passion'' was revived by Mendelssohn in 1828 after years of public neglect.
Another type of intercession has become a thing of scorn to musical purists. It involves a skillful composer's touching up - or even overhauling - a masterwork to make it more palatable to a contemporary audience. I refer specifically to Mozart's reworking of Handel's ''Messiah,'' though another equally dramatic example would be Rimsky-Korsakov's overhaul of Mussorgsky's uncompromising ''Boris Godunov.''
In both cases, respected composers looked at a manuscript and deemed the work important enough to sweeten the inherent astringencies so as to bring the work to a new public's attention. Mozart was making out-of-fashion baroque music fashionable. Rimsky-Korsakov made demanding, uncompromisingly orchestrated music less remote. The revised versions of both of these important compositions are currently reviled by purists, and somehow performing institutions have followed suit.
Unquestionably, the original works are extraordinary achievements: The original versions are the preferred ones. Yet the beauties and appeal of the reworked versions should not be ignored. Of late, it has become impossible to hear Rimsky-Korsakov's version of Mussorgsky's ''Boris,'' except on records.
This past weekend the Mozart reworking of Handel's ''Messiah'' (known as ''Messias'' and performed in German) was given a pair of performances at the Mostly Mozart Festival at Avery Fisher Hall, Lincoln Center. It afforded an unnecessarily rare chance to hear this baroque marvel through the ears of a later genius.
So elaborate was Mozart's reworking that he chose to include this effort on his list of compositions (K. 572). He clearly loved ''Messias'' and wanted his audiences to love it, too. He enriched the orchestra (adding trombones, bassoons , horns, clarinets, flutes) to accommodate their sound tastes, reordered the score by reassigning some solos to different voices, and reorchestrated and in many cases actually recomposed the piece, using Handel as framework.
It makes no pretense to being Handelian. Many of the choruses take on a near-operatic intensity when Mozart begins the music with the quartet of soloists, slowly building up to a full choral entry. But in most cases each number is truncated. There is no organ (the hall this verison was written for had none), and throughout there is Mozart's wonderful sense of balance between strings and winds, and between orchestra and singer or chorus.
The solo work for Mostly Mozart was of a high order: The ravishing, limpid soprano of Benita Valente; the easy, resonant lyricism of John Aler's tenor; the imposing, youthful bass of Jan Opalach; the small-scaled yet pliantly artistic mezzo of Shirley Love.
Joseph Flummerfelt's New York Choral Artists was in top form, and conductor Gerard Schwarz offered a vigorous, propulsive account of the score, recognizing at all times the Mozartean bent of the music. Giulini resignation
The announcement that maestro Carlo Maria Giulini has resigned his post as music director of the Los Angeles Philharmonic for health reasons leaves a void on the American orchestral scene. The maestro has agreed to fulfill a few of his weeks next season, and thereafter to guest conduct for two weeks a season as well as record. Plans to produce another opera in the manner of the hugely successful Verdi ''Falstaff'' last year are, presumably, canceled.
The sort of noble, heartfelt, deeply serious musicmaking that Giulini represents has been welcome and needed in the US today. He represents an older school of musicianship that puts personality at the service of the music, the sort of musician who has devoted a lifetime to pondering the meaning of each piece he chooses to conduct.
Giulini's may not be the sort of all-purpose musicianship American orchestras need today to fulfill long seasons of subscription concerts. Mehta to succeed?
The most outlandish of the inevitable rumors now circulating about maestro Giulini's replacement has it that Zubin Mehta will give up the New York Philharmonic after four years tenure and return to the Los Angeles Philharmonic: His 14 years there put that orchestra on the map, and a return at this juncture would be a very unlikely step backward in his career. Major symphony orchestra conductors almost never return to reclaim podiums.
Concurrent with this rumor has been the public airing by New York Philharmonic players of increasing dissatisfaction with their music director. This comes on the heels of an announcement by CBS Masterworks that the Philharmonic will no longer figure in its recording plans. Mr. Mehta has tried hard to put a stamp on the Philharmonic and to make the orchestra respond to his leadership.
He may have his moments of apparent indifference on the podium, but when the group is in one of its collective ''moods,'' no conductor can make them play like the great orchestra they are capable of being. At other times, such as during the performance of Schonberg's ''Gurre-Lieder'' this season, Mehta and the Philharmonic do make fine music together. The problem is that the orchestra's so-what attitude - exemplified by sloppy posture and whispered discussions during performances - exudes a laxity and indifference audiences cannot help but notice.
Granted, playing for the noisy, fidgety, ''I only want to hear war horses'' crowds that populate Avery Fisher Hall week after week can be enervating. Also, despite a total rebuilding of the interior, Avery Fisher Hall retains an acoustic that neither flatters an orchestra nor allow players to hear each other on stage. The season schedule is uncommonly demanding. The 33 subsription weeks are filled with different programs that only recently have begun to overlap, despite the alternate-week subscription series.
No one benefits from any of these difficulties. Yet it is unfair of any orchestra to blame its music director for shortcomings until it has cleared up its own inner disciplinary problems. If the players do not treat the job with all the respect due the music; i.e., if they do not play as if this musicmaking were the most important thing in the world - the players must shoulder the blame for the lassitude that ultimately pervades the ensemble. When the orchestra involved is just about the highest paid in the land, the players need to prove their worth before they begin publicly questioning their music director's abilities.