A conducting assignment kept Gunther Schuller from personally accepting the $5,000 first prize in the 10th annual Kennedy Center Friedheim Awards yesterday afternoon, but he was well represented musically by his String Quartet No. 3, which sounded like an instant classic.

Atonal in structure, splendidly varied in style and deeply emotional in expression and impact, the quartet received by far the longest and loudest applause of the four pieces played at yesterday's concert, which was also the final round of a competition for best new instrumental chamber music that began with 147 entries. For once, the three judges agreed with the audience on first prize -- perhaps because all of them (pianists Michael Boriskin and Dina Koston and cellist Bonnie Hampton) are performing musicians, regularly in touch with the public.

The competition's $2,500 second prize went to Barbara Kolb for her "Millefoglie," an elaborate, 20-minute work for a computer-generated sound track and a nine-piece chamber ensemble that virtually amounted to a miniature orchestra.

A similar ensemble (13 pieces and no sound track) performed Tod Machover's evocative "Nature's Breath," which took the $500 fourth prize. The absence of a sound track was mildly surprising (though not as surprising as the fact that this work came in fourth), since Machover, a professor at MIT, is one of the leading living exponents of electronic music. He also was unable to attend the concert, being intensely at work on his opera "Valis," based on a science fiction novel and reportedly featuring a multitude of electronic sound and visual effects. The opera was commissioned for the 10th anniversary of the Centre Pompidou in Paris.

The third prize ($1,000) was won by a highly inventive, often epigrammatic string quartet curiously titled "Fumeux Fume," composed by Steven Mackey. Mackey began his musical career as a specialist in early music, performing on the lute, and this orientation may explain the title of his work, which was also the title of a rondeau by the 14th-century French composer Solage. The composer has described the two-movement work as the musical equivalent of a short story (the first movement) followed by five short poems that comment on the material of the short story (the second movement).

It is a brilliant survey of the varied textures, accents and dynamic sequences available to four highly coordinated string instruments. With Schuller's work, it testifies to the continuing vitality of the string quartet medium after more than two centuries of intense cultivation. And it contrasts sharply with the Schuller quartet in almost every respect except the fact that both pieces are composed for two violins, viola and cello.

Schuller, who was president of the New England Conservatory, founder of that institution's highly popular ragtime ensemble and developer of the "third stream" concept attempting to form links between jazz and classical music, was by far the best known composer on the program, and his quartet proved that his widespread recognition is not unearned. The opening movement is intensely dramatic, with sharply contrasting moods. The slow movement, an excursion into pure instrumental song, exudes a kind of peace rare in contemporary music, and particularly in music based on 12-tone techniques. The finale is technically brilliant -- uncompromisingly modern while it flaunts affinities to Beethoven and Schubert.