The Smithsonian Chamber Players delved into Bach, or to be more precise, into Bachs -- J. S., J. C. and C.P.E. -- at Baird Auditorium last night, effecting the transition from the baroque to the classical with humor and style.

Numbering 21 musicians these days, the Chamber Players have reached the proportions of a respectable baroque orchestra, and their talent and instrumentation gives them the flexibility to explore almost the entire 18th-century instrumental repertoire.

Last night's concert opened modestly with a delightful Trio Sonato attributed to J. S. but rumored to be, in fact, by his pupil, Goldberg, of Goldberg Variation fame. If this is the case, he did his mentor proud, for it is a marvelously inventive piece, full of insouciant charm.

The interest of Johann Christian's Quintet for flute, oboe and strings lay entirely in its performance and in the distinctive sounds of the wooden flute and baroque oboe spinning out the ornamental patterns of the music's superficial veneer.

The momentum and lightness that made the first Orchestral Suite such a pleasure got a little out of hand in the Third "Brandenburg" Concerto which, at times, sounded frantic.

A symphony by C.P.E. closed the door decisively on the baroque and pointed in new directions.