The concertos of Bach do not require the touch of the virtuoso the way, let us say, Brahms' concertos do--though the rigor and intensity of a Heifetz or the late Glenn Gould hardly does them any harm.

Still, fairly modest versions of Bach retain a certain allure--like the ones played last night by the Washington Chamber Orchestra at the Wolf Trap Barns. This creditable local group may not follow the current vogue in using authentic instruments but it does function on the chamber scale that was most common to Bach. For the B-minor suite for flute and orchestra there were seven players and in the glittering Second Brandenburg Concerto the aggregation reached its numerical peak, 10 players (it would be hard to play it with fewer).

Perhaps the finest work of the evening came at the beginning, with the second suite. Flutist William Montgomery had plenty of technique and in several of these bracing dance movements he and the other players phrased with splendid pointing--in the polonaise, for instance.

The remaining works--the second Brandenburg and the E-major violin concerto--did not glow with the confident excitement they might. Ensemble was good; intonation, on the whole, was solid, but the music was played more safely than sublimely. That assured euphoria that suffuses Bach when he is in this mode was tempered with sober caution.

Timothy Baker was the worthy soloist in the violin concerto.