Christopher Kendall seemed to do everything last night in the Kennedy Center Concert Hall. For much of the evening, he was playing very old music on the lute, other plucked strings and occasionally a tambourine as a member of the Folger Consort, Washington's (and one of the world's) leading early music ensembles. But for two extensive segments, he was standing before the 20th Century Consort, one of Washington's (and the world's) leading avant-garde ensembles, conducting music of our own time.

At one point, he played "O Come Emanuel," a timeless Christmas melody assembled in the last century from ancient plainchant motifs, on a set of bells. Then he was quiet for a few minutes while Jubilate, a fine ensemble of eight voices, sang the haunting melody. And a bit later, he was conducting the same melody as part of the second movement of Respighi's "Botticelli Triptych."

As director of the 20th Century Consort, Kendall devised an ingenious program that featured modern works embodying ancient melodies that the Folger Consort had performed earlier in the evening. Besides the Respighi spectacular, these included two works of Vaughan Williams: Fantasia on "Greensleeves" and Five Variants on "Dives and Lazarus."

This was certainly one of the season's most imaginative Christmas concerts, and it was presented by Millennium, the only ensemble capable of handling the ancient and modern sides of the presentation with equal authenticity and stylistic expertise. Millennium is a Washington-based consortium of chamber ensembles whose various members are specialists in musical styles spanning 10 centuries. Besides sponsoring a festival each summer on Martha's Vineyard, programs on various college campuses and other concerts, it is now producing a 10-part television series on the history of music. Last night's program explored the extremes of its vast repertoire and found intriguing connections between them.

For the occasion, the 20th Century Consort was expanded to a chamber orchestra, augmented by members of the National Symphony, and Kendall drew from it finely textured readings of the conservative modern repertoire. The Folger Consort and Jubilate drew most of their material from England and Italy. They were impressive throughout but particularly in their final segment, which included Italian polyphony, dance music and the exquisite, folk-based religious music called "laude."