Friday night's program of the Library of Congress' free Summer Chamber Festival featured Mozart, Schumann and George Rochberg and -- against all odds -- Rochberg proved to be the winning entry. His Trio for Clarinet, Horn and Piano, composed in 1948 and slightly retouched in 1980, is tonal, rhythmically exciting and highly accessible. Rochberg was 30, recently demobilized from the army and bursting with ideas.

The first movement is half tarantella, half march and all neoclassical brio. Paul Hindemith is a major and fruitful influence here, but the solo cadenzas are unique and arresting. The adagio opens with a long, mysterious passage in parallel motion for the two winds, which converse separately from the piano, though they share the same material. It is laden with nostalgia, magic and not a little pain.

The finale is parodistic. Its many humors include an aborted fugue in waltz time and a snatch of "Non piu andrai" from "The Marriage of Figaro." Rochberg invents dazzling sonorities for all three instruments but especially for the French horn, which keeps disguising itself, chameleon-like, producing every conceivable sound except an ugly one.

Hornist Anthony Cecere was a prodigy of virtuosity, and clarinetist Loren Kitt and pianist Edmund Battersby gave as good as they got. This trio is too little performed. By now it should be an American classic.

Rochberg, a young 69, was in the audience and shared an ovation with the performers.

The program opened with a beautifully sculpted account of Mozart's Clarinet Quintet and closed with Schumann's thickly scored Piano Trio No. 1 in D Minor.