J. Reilly Lewis and his Washington Bach Consort brought the 17th annual Bach festival at the Church of the Ascension and St. Agnes to a spirited close last night. Showing a notable leap in the polish of its performance--a possible outgrowth of its German tour last June--the Consort seems to be working steadily toward interpretations of much greater depth and force.

Always a conductor of enthusiasm, Lewis displayed a new maturity in the control of his forces. His capacity to shape the music into a unified and concentrated whole has moved forward dramatically since last year's festival. As his conducting of the Ascension Oratorio, BWV 11, revealed, he has learned to construct a rhythmic framework that holds like steel against the multiple stresses of Bach's driving lines.

At the same time, Lewis is discovering, and obviously enjoying, the supple melodic interplay that can take place within such a firm structure. While maintaining its rhythmic strength, his direction never seemed rigid. The various instrumental and vocal voices unfolded in a spacious manner and with a previously unheard clarity that also confirmed Lewis' increasing mastery.

Lewis contributed a lively organ part in the two Sinfonias included in the first half of the program. In the opening Sinfonia from the first part of Cantata 35, his handling of the nonstop organ role that alternates between continuo accompaniment and vigorous display passages proved a special pleasure.

Associate conductor R. Benjamin Dobey's direction of Cantata 44 suffered from a ragged start and a weak beat, underlining the need for the kind of strong rhythmic propulsion that Lewis offered in the other works. The sound of the chorus, apart from a few harsh high tenor entries in the Ascension Cantata, was marked by an exceptional smoothness and expressiveness. The orchestra offered consistently sensitive support as well as some lovely instrumental counterpoint to the vocal lines.

The evening's roster of capable soloists included soprano Nancy Krohn Young, mezzo soprano Jeanne Haughn, baritones William Kugel and Benjamin Dobey, tenor Robert Petillo and countertenor Derek Ragin, whose clear sweet sound showed promise if not always control.