Just prior to the Washington premiere of Lukas Foss' "Solo Observed" at the Kennedy Center Concert Hall Saturday night, Charles Wadsworth, artistic director of the Lincoln Center Chamber Music Society, apologized for the lateness of the hour. The program didn't begin until nearly 10, after the San Francisco Symphony finished performing in the same hall. His remarks were appreciated but unnecessary; the audience probably would have stayed until dawn to hear clarinetist Gervase de Peyer, violinist James Buswell and cellist Fred Sherry.

Pianists Foss and Wadsworth nimbly tackled the eight sections of Brahms' Variations on a Theme by Haydn for Two Pianos, Op. 56b. Foss returned with de Peyer and violist Nobuko Imai to present Mozart's unique Trio in E-Flat Major, K. 498. De Peyer's tone, particularly in the final movement, was exquisite.

Foss' "Solo Observed" is quite aptly named, for the pianist states a motive, checks his progress, begins anew and builds intensity with ever-developing inner voices, while the cellist, vibraphonist and organist sit idly by. Upon entering, they insert decorations, barely containing the piano's unending vortex of eighth notes, which grind to an abrupt halt, ending the piece.

James Buswell's full-bodied violin playing led the way in Beethoven's Septet in E-flat Major, Op. 20, for strings and winds. Conceived more to entertain than to edify, this divertimento's jaunty character reached its peak in the energetic Scherzo.