Yesterday afternoon's concert by the Washington Bach Consort in Dehlgren Chapel of Georgetown University was a fascinating mixture of sounds and forms.

There was the cantata, also properly called a motet, "O Jesu Christ, mein's Lebens Licht," with voices and six wind instruments: a piccolo trumpet, two flugelhorns, a real sackbut and two trombones. The resulting blend of voices and winds is one of Bach's distinctive achievements. With excellent singing and playing under Reilly Lewis's direction, it came out ideally.

Another stellar episode came in Jody Gatwood's superbly poised account of the D Minor Partita for solo violin.

One of the ultimate tests for violinists, the Partita emerged from Gat-wood's knowing mind and fingers with beautiful tone, no sense of strain, and filled with style that rose to true marvels in the gigue and chaconne. No wonder the audience rose to its feet in tribute at the close.

Lewis, who has in Dahlgren Chapel a jewel for performing Bach, with its intimate size and notable acoustics, has a particular affection for Bach which he spreads through his listeners with welcome, friendly comments. The program, which closed with the short Mass in A, included a somewhat unfortunate account of the double concerto for oboe, violin and strings. Problems of tone and intonation on the baroque oboe and violin were too frequent to permit much enjoyment.