For a moment, it looked like a traditional recital. William Hellermann walked on stage impeccably clad in white tie and tails, sat down, closed his eyes meditatively and held his hands folded in his lap for a moment before beginning the music.

What was different was the instrument, which had been carried on stage ceremoniously a few minutes earlier, unzipped from its quilted carrying case, and carefully adjusted for the performance. It was a swivel chair - wooden, with arms - the kind found in thousands of offices, though for concert performance its squeakiness may have been enhanced with rosin. Hellermann performed his entire composition "Squeek" (basically subtle variations on a three-note motif) by rocking back and forth in the chair, carefully controlling the sounds it produced.

"Squeek," which Hellermann calls "a rock piece," was one of the 50-odd (some very odd) compositions presented in a recent festival of "New Music, New York" held at the Kitchen, an experimental arts center down in SoHo, one of the more seedy sections of the Big Apple. Not the most compelling work heard in the festival, it was one of the most entertaining, and it exemplified some trends in new music.

It was, for example, as much a theatrical as a musical experience. It used standard audience expectations as leverage to produce its special effect - by the simple expedient of denying and, in a way, ridiculing those expectations. Besides being music of a sort, it was also a sort of criticism - social criticism and music criticism.

Above all, it was a prime example of minimalism, which is the trend, if there is any single trend, in post-avant-garde music. Hellermann's instrument was wooden, and could have produced all sorts of percussion effects if he had chosen to explore them, but he insouciently declined the gambit. The chair is also capable of producing a variety of sustained notes, by swiveling around rather than rocking back and forth, as anyone who has sat in a squeaky swivel chair is well aware. But Hellermann was content to use, over and over again, the handful of notes he needed to make a certain calculated effect.

"Squeek" is only a small part of what was happening during those 10 evenings, but it serves as well as anything to establish the basic point of the festival: the stately, millennial march of the Western Musical Tradition is being challenged and turned around in a few grubby blocks of lower Manhattan.

It remains to be seen whether that tradition will paus in its stately, millennial march to pay serious attention to the challenge - it has been challenged so often in the last few generations, and it has other things to do; things like selling tickets and making the 50th (or is it the 150th?) recording of "Scheherazade."

But some of the composers who were presented at the Kitchen are beginning to find a place within that tradition. At least, their names are now enshrined, along with those of Bach and Mozart, Stockhausen and Berio, in the composer's section of the Schwann Record and Tape Guide, the industry's standard index of those who have achieved a degree of immortality by being recorded.

Hellermann is a member of that charmed circle (though not with "Squeek," which would need video recording to make its effect), and so are a handful of the other composers who were presented in the festival: Robert Ashley and Pauline Oliveros, whose work is deeply admired (and sometimes imitated) by some of the younger composers; Steve Reich and Philip Glass, who are achieving commercial success of a sort and attracting attention outside the small world of SoHo.

The list is incomplete, and the Schwann is only a rough index of status, not of who has been recorded. One of the labels that features the music of SoHo composers, Lovely Music, has not yet made it into Schwann - though others, such as CRI, Tomato and 1750 Arch are in there, and some of the composers are on major American labels such as Nonesuch, Odyssey and Turnabout. Steve Reich has made it on Angel and Deutsche Grammophon - bit international labels - and SoHo composers ave been heard in lively conversation on whether or not he has "sold out."

Reich is probably the best-known of the SoHo composers, with Glass (whose opera, "Einstein on the Beach," has just been recorded) a fairly close second. Both were featured in the gala opening concert of the Kitchen's series. They have some qualities in common (and in common with some other SoHo composers) that make them seem members of a new "school" of composition - at least to an outsider. Both composers, and some of their fans, insist that they are quite different, and they are if you look at them from close up. But compared to Beethoven, or even Varese, they seem very close together.

A hostile critic could say that what they have in common is the use of boredom as a basic structural principle - but again, that is the view from a distance. What is undeniable is that their music moves very slowly by traditional classical standards, making Anton Bruckner, for example, seem a hyped-up chatterbox. Reich will start a piece with a very simple motif repeated over and over again, slowly, obsessively, for what can seem to be hours on end but is more likely to be only minutes. Then, a new element will be added and, a few minutes later, another, while the old elements continue their obstinate repetitions. If you compare the beginning and the end of a Reich piece, as you can easily do on a recording, you will find that a lot has happened. But it happens so gradually as to be almost imperceptible. Or rather - and this is one of the points of the music - you have to readjust drastically your modes of musical perception to observe it happening.

What is happening, really, is that the Western musical tradition is being abandoned - or at least subjected to severe criticism. As it has evolved, particularly in the last two centuries, that music has had a basically dramatic structure: the struggle of one motif against another, the wandering of a theme from one key to another with an underlying feeling of suspense (usually subliminal, but no less powerful for that) about whether and how it will get back safely to its home key. That system had been used so much by around 1900 that that it was approaching artistic bankruptcy, and the history of music in the 20th century is a history of attempts to find new ways to organize large musical structures that will communicate with an audience.

Most of those earlier experiments - primitivism, serialism, impressionism and expressionism, electronic music, aleatory music and improvisation, for example - have left some traces in what was going on during the festival at the Kitchen. But along with minimalism, which is its cousin, primitivism (now rechristened "third-world music," and with a new depth of appreciation implicit in the revised title) seemed to be the most interesting trend. Both minimalism and third-world music tend to avoid the pseudodramatic structures of Western classical music and opt instead for a sort of immobilism. Rather than charge toward a climax like the "William Tell" Overture or the Second Symphony of Sibelius, this music tends to just sit there, and you are not ready to appreciate it until you can perceive that the same note, or chord, or melodic or rhythmic pattern, repeated 100 times or more, stops being the same at some point in the process. In a sense, this is mucis for meditation, and if you pay attention, it leads to a refinement of perception that is not needed for music as assertive and eventful as Beethoven's Fifth. On the other hand, Beethoven, more than most classical composers, may have been on the track of something similar; if only there weren't so much harmonic motion in the four-note motif of his Fifth, the three-note motif in the scherzo of his Ninth. But unlike Beethoven, this music tends to be restful, and at its best (for example, in Jon Hassell's "Fourth World Sketches" and Philip Corner's "Gamelan," which were performed at the festival, or in Tom Johnson's "An Hour for Piano," which is recorded by Lovely Music) it achieves an unworldly sort of transparent beauty.

Taped pieces and computer-assisted pieces were abundant at the festival. Some were routine, some approached or passed the pain threshold in volume, and there were some striking sound effects as well as quite a bit of collage. One composition that lingers in memory is the 14-minute "Voices Within" of Laurie Spiegel, which brought a sense of classical form to the tape medium with striking effect.

One reason for using tape - or for composing pieces which can be performed by the composer, perhaps with a few friends - is economic. Write an opera or a piece for orchestra without a commission, and you may spend the rest of your life wondering how it would really sound because it is too expensive to perform. Pauline Oliveros solved that problem and provided one of the festival's finest moments by making the audience the performers in a simple but marvelously effective group improvisation, each member of the audience singing a tone, listening to the others, and choosing another tone with which to harmonize. It's a risky business, but this was a talented audience and the effect was beautiful.

Two of the composers in the festival are listed in Schwann not as composers but as jazz performers: trombonist George Lewis and trumpeter Don Cherry. Lewis improvised, exquisitely, a duet with a computer; Cherry played the duzon goni (an African hunter's harp) and was wildly applauded for a performance that was a triumph more of personality than of music. Their presence in the festival, as well as that of Garrett List and the A-1 band, who played a brilliant, high-spirited and very eclectic jazz set, illustrates one of the things that are happening in SoHo: the old, rigid distinctions between popular and classical, jazz, rock and ethnic idioms are melting away and young composers are just making music, appropriating any idiom that suits their purposes.

SoHo's ability to assimilate any musical idiom was shown most decisively, perhaps, when pianist-composer Ivan Tcherepnin played his "Fetes," which was the kind of thing that SoHo denizens sometimes call "uptown music." Composed in C major, it was a chorale, prelude, triple fugue and coda on "Happy Birthday to You." The idiom was not exactly new - but since the heydey of John Cage, very little is completely new. The experimenting has been done, it seems, and now it is time to integrate that expanded musical vocabulary into something that communicates. Many hands in SoHo are busy at that work, and after the kind of music academic composers have been producing in recent generations, the effort is truly revolutionary.