There are more than 215 Bach cantatas. Taking as a rough average six numbers per cantata, the Bach enthusiast is faced with 1,290 choruses, recitatives, arias and duets to digest. That's enough to give anybody dyspepsia. The Bach Aria Group was formed to help the bewildered by selecting recital anthologies ranging through all of Bach's vocal works.

Saturday night at the University of Maryland it accomplished its mission yet again. A chamber group, it excludes the choruses that usually open and close these cantatas and concentrates on the intimate chamber music of the central arias and duets.

Proof of the group's success is that it has been around for 40 years.

In earlier years the participants included such operatic heavyweights as Eileen Farrell and Jan Peerce. Saturday's singers were not so famous or so glamorous, but all four served Bach better. The vocalists are only half of this group; the instrumentalists, as is appropriate, are given equal billing.

The major item on Saturday's program was the secular cantata "Aeolus Appeased," minus its flanking choruses and its best aria (which requires trumpets, horns and drums). The group performed this and the other vocal numbers so well that one wanted more arias in place of the less-than-authentic trio sonata that opened the second half of the program, despite the fine playing of flutist Samuel Baron and cellist Timothy Eddy.