William Schuman, best known as a composer of orchestral music, was on hand Tuesday night in the Library of Congress to hear some outstanding performances of his vocal works. The concert was given in honor of Schuman's 75th birthday -- somewhat belatedly, since that happened last August -- and the evening's highlight was, appropriately, the poignant cycle "Time to the Old," set to three poems of Archibald MacLeish.

"Only the old know time: they feel it flow/ like water through their fingers," MacLeish's text proclaims. Schuman's music -- intensely chromatic and full of vivid dramatic hushes, pauses and terror-tinged melodic leaps -- intensifies the effect of the already tense words. There are moments of calm -- an old man dozing off on the lawn on a warm summer afternoon; an old couple who have grown together so fully that they communicate without talking.

But the shadow of death hovers in the background of each poem and takes the spotlight at the end. The music is superbly dramatic and the emotions are subtly shaded. Soprano Rosalind Rees and pianist Gary Steigerwalt gave it a brilliant performance. Steigerwalt also soloed impressively in the "Voyages" cycle for piano.

The rest of the program was given by the University of Maryland Chorus Chamber Singers, under the direction of Paul Traver, and the interpretation was (as usual with this group) close to perfection. Every syllable came across with total clarity, the tone was bright and beautifully balanced, and the technique was of virtuoso quality.

Rees joined the chorus in Prelude for Voices (with a text by Thomas Wolfe) and "Perceptions," a cycle of short, epigrammatic excerpts from Walt Whitman's work.

The chorus sang alone in "Carols of Death" (also by Whitman) and the witty "Five Rounds on Famous Words," with texts based on proverbs strung together and set in polyphonic style: "Look before you leap. A stitch in time saves nine, and an ounce of prevention is worth a pound of cure," for example, in the final number, "Caution."

Schuman's choral writing is brilliant. The music is always at the service of the text, and clarity is a prime virtue, but the range of expression is wide and the colors are almost as vivid as in his orchestral music.

The interpretation could not have been in better hands than those who sang this music Tuesday night.