Guillaume Lekeu (1870-1894) is hardly a household name, even in his native Belgium, but he stands high on the appallingly long list of composers who died too young. Friday night at the Library of Congress, the audience heard an inkling of the promise left unfulfilled when he died, one day after his 24th birthday, leaving unfinished a Quartet in B Minor for Piano and Strings.

Performed with intense fervor and precise technique by the American Chamber Players, the two movements of that quartet (the second was finished by his teacher, Vincent D'Indy) fulfilled the composer's description: "A poem of the heart, where a thousand feelings collide, where long appeals to happiness follow cries of suffering."

There were a few problems--not in the performance but in the music's unfinished condition and the noisy, disruptive arrival of latecomers who broke the mood between the tight-knit first and second movements. Still, it dazzled listeners, perennially the most sophisticated music audience in Washington.

The program concluded with Schubert's Octet in F, one of the most engaging entertainments in the chamber music repertoire, a perfect balance of string and wind textures, a riot of lighthearted melodies and Viennese dance rhythms with just enough depth to make a contrast and an ominous introduction to the last movement, which turns out to be a joke. There were moments of imbalance at the beginning, particularly involving the horn, but they were quickly corrected in a performance that won a long, richly earned standing ovation.