Mozart's "Ave Verum Corpus," which the Master Chorale of Washington sang toward the beginning of its concert at the Kennedy Center Concert Hall yesterday afternoon, is three minutes of musical perfection. Moreover, as if to shame those composers, before and since, who have made a fetish of bigness and complexity, the perfection of the "Ave Verum Corpus" is as simple, direct and sweetly humble as a child's prayer, without an extraneous or virtuosic gesture.

Indeed, this is a work that can be sight-read by any chorus, played by any amateur string quartet, even fumbled through haltingly by a first-year pianist, and it will still, inevitably, bring a lump to the throat and a welling to the eyes. It is music of absolute clarity and serenity, neither loud nor soft, presenting no technical difficulties whatsoever to those who would take it on. But distilling such simplicity is never an easy task for a creative artist, and only the best of them can carry it off. Remember the philosopher Pascal's remark that he had no time to write a short letter and so he had written a long one? In the "Ave Verum Corpus," Mozart found time to write posterity a short letter -- then wrote with all his heart.

The Master Chorale program began with a "Te Deum" dating from Mozart's 13th year. Not surprisingly, the composer was still learning his craft at that tender age, and this particular work seems to have been fashioned after a similar piece by Michael Haydn, a good model. Under the direction of Donald McCullough, it received a crisp, vigorous performance -- all organ, brass, timpani and joyful hymning.

Mozart's great, problematic "Requiem," which was left unfinished on his death in 1791, closed the afternoon. McCullough elected to perform a 1993 reconstruction by the musicologist Robert D. Levin in lieu of the familiar -- and notoriously corrupt -- "completion" by Mozart's student F.X. Sussmayr that has been the standard for more than two centuries.

Some of the worst of Sussmayr's vulgarities -- the stupefyingly banal, quasi-rockabilly triplets in the accompaniment of the "Sanctus," for example -- are blessedly removed, and there are some impressive new fugal passages. Still, nobody can match up to Mozart, and there can be no doubt that the "Requiem" slides downhill after the great cry of "Homo reus" in the "Lacrymosa," traditionally said to be the last music the composer ever wrote.

Unfortunately, the performance was stronger on passion than it was on polish. The chorus sang out mightily much of the time, and details were too often lost in an undifferentiated loudness. One had the sense that the singers' splendid urgency could have been directed toward a more coherent objective, that Mozart's melodies could have been molded and shaped with greater subtlety and dynamic contrast. (Curiously enough, the orchestra seemed much more responsive to McCullough's direction than did the singers, an unusual state of affairs at a choral concert.)

The soloists were mostly admirable. Baritone Grant Youngblood, with his calibrated breath control in the taxing opening line of the "Tuba mirum," made an especially strong impression. Mezzo-soprano Victoria Livengood's biography in the program booklet mentioned that she has won acclaim for her roles as Bizet's Carmen and Saint-Saens's Dalila; rarely has Mozart's religious music sounded so fiercely sultry. Matthew Chellis brought a bright throb to the tenor solos, while soprano Cheryl Evans handled her passages with unusual fervor.

All in all, it was a joy to hear this music -- but there is more in it than was let on yesterday afternoon.

Donald McCullough 's conducting brought more responsiveness from the orchestra than from the Master Chorale during the Kennedy Center concert.