For the past 10 years, a loosely defined ensemble called Essential Music has been presenting and advocating what it calls "new and neglected music of the American experimental tradition." Last weekend, EM, led by its founders, John Kennedy and Charles Wood, reprised and premiered a diverse selection from its ample repertoire, works which roughly reflect the creative fallout of John Cage and Henry Cowell. What this aesthetic boils down to is avoiding "schools", such as minimalism and serialism, and embracing what Cage referred to as "the world of X, chaos, the new science."

Morton Feldman certainly fits that bill, and his enchanting Between Categories (1960), for pairs of violins, cellos, pianos, and chimes, lulls the listener into exploring subtle shades of quiet and slowness. The performance was ravishing: exquisite sounds seemed to hover glowingly before your rapt ears. John Cage's Two2 was likewise a slow excursion into a quiet realm, yet more enigmatic if more frustrating.

The 45 minute composition, consisting of understated chords relayed between two (unprepared) pianos, is aggressively anti-dramatic: Battling your boredom and going beyond it is part of the experience. Cage was perhaps being cagey when he admitted to William Duckworth in Talking Music, "I believe in things that are inexplicable," but here he genuinely practices what he preaches.

Duckworth is also a worthy composer, and his dynamic Revolution for huge percussion ensemble and piano, was one of the better newer pieces presented, as was Kyle Gann's Snake Dance No.2. Gann, who's better known as the Voice's new -music critic, is no composer manqué. His work, inspired by the pulse-shifting of Native American music and the polytempos of Conlon Nancarrow, is a thrilling intermeshing of rhythmic cells.

Two of EM's favorite "finds," Johanna Magdelena Beyer (1888-1944) and William Russell (1905-1992), were also represented. Beyer, Cowell's assistant--who took over his New Music Editions while he was doing time in San Quentin on a homosexual morals charge--wrote disarmingly odd pieces, and Music for Spheres is no exception. Scored for lion's roar, triangle, two violins, and a cello, this is a ghostly work, suggesting both celestial clockwork (the cello's ostentatious ostinato) and galactic nebulousness (undulating violins).

Russell's tongue-in-cheek Music for Minsky was performed with great verve, as a gay go-go boy, Angel Davis, swerved his hips and a magenta-gowned librarian-type, Miss Joan Marie Moossy, stripteased. At the very end, a nude and busty Penny Arcade shouted, "That's Burlesque!"

One of the more successful coups of this three day festival was not by an American composer but by German Dadaist Kurt Schwitters. His Ursonate (1922-1926), a four-movement work made entirely out of German phonemes strung together and pulled apart in sundry combination, is a masterpiece of pure nonsense made meaningful through musical form. Musical sequences are built through repetition, fragmentation, interpolation, variation, pauses, and so on (the first movement is a rondo with four motifs). The whimsical piece was given an enthusiastic , humorous performance by a madly gesticulating Dary John Mizelle, who convinces you that his Sprechstimme gibberish is the most important thing in the world. Mizelle is himself an accomplished composer, as evidenced by his flute and percussion Suite, the most tightly composed piece of the entire series.

A much less successful "sound text" was Cornelius Cardew's The Great Learning. Unlike Ursonate, which creates a meaningful musical syntax out of silly syllables, this unfortunate offering renders incomprehensible a perfectly sensible Confucian text translated by Ezra Pound. The music amounts to nothing more than an annoying 45-minute drone. It left denizens of the Downtown music scene wandering about like zombies off the set of Night of the Living Dead.

Wood and Kennedy are facile experimentalists in their own right. Woods Three fields to a Tree is a quaint, lovely trio for three electric teapots that whistle wistfully until their steam runs out. Kennedy's The Winged Energy Of Delight is a delightful piece for perky Chinese cymbals and toy piano. Wood fared less well with Red Grass Appearing, an interminable quartet for whimpering whistlers, as did Kennedy, whose Full Measures of Devotion sounds like a very unexperimental background music for a Caribbean cruise commercial. More of James Tenney (whose short but dense deus ex machina for gong and digital delay was performed) and Robert Ashley (whose sardonic aria Odalisque was sung beautifully in Italian by Thomas Buckner) are in order.

Although EM doesn't always succeed in playing what's essential, its unwavering commitment to the experimental is vital in a contemporary music milieu where the lack of invention is amply rewarded.