Dionysus and Apollo shared a stage Sunday afternoon at the Kennedy Center Concert Hall, where the Washington Chorus presented two radically different 20th-century masterpieces: Igor Stravinsky's "Symphony of Psalms" and Carl Orff's "Carmina Burana."

The Stravinsky work is pristine, modernist and cerebral; some will always find it cold. For other listeners, it is one of the supreme devotional works of the 20th century, three psalm settings that not only carry the weight of centuries of musical and religious traditions but also extend those traditions into exhilarating and unfamiliar territory. After 75 years, the "Symphony of Psalms" still seems new and strange and austerely beautiful.

Unfortunately, it is also very difficult to play and sing, and the Washington Chorus and Orchestra failed Sunday on both counts. The collective diction was mushy, the rhythms were imprecise and much of the instrumental playing was little short of abysmal, with glaring mistakes every few measures. The whole performance seemed anxious and under-rehearsed, this in a piece that demands clarity and exactitude above all. Only in the final "Laudate" -- awed, hushed and near-motionless -- was there any sort of unanimity.

"Carmina Burana" was better, although I think another rehearsal or two might have improved matters enormously. Orff's ever-popular cantata is everything the "Symphony of Psalms" is not -- pagan, primal and a work in which sheer exuberance will go a long way toward putting it across. Robert Shafer's urgently propulsive direction (he seems to mistrust pauses) was not out of place in a piece with such an emphasis on steady pulsation, and he drew an enthusiastic response from his forces. The Children's Chorus of Washington, in particular, sang with bright jubilance.

It was left to the soloists to make the strongest impression of the afternoon. Stephen Powell proved a terrific baritone, absolutely at home in whatever he was called upon to do -- croon, chant, proclaim, woo -- with just the right mixture of impetuous ardor and fatalist humor. Christopher Pfund stepped in at the last minute to replace tenor Michael Forest in Orff's comic-lachrymose aria of the roasting swan, where he combined the movement's inherent grotesquerie with some dapper musicianship. Maire O'Brien was fresh and sweet in the soprano arias, and she has both the stratospheric high notes and the raw courage to take on the solo "Dulcissime!," one of the most difficult and brutally exposed half-minutes in the repertory. Indeed, if the composer had asked the soprano to go much higher, only dogs would have been able to hear her.