The Bach Society Orchestra played its first concert of the year with verve and discretion, though the fare offered was surprisingly light. Perhaps the orchestra's conductor, John Harbison, is thinking of the taxing problems he will face in preparing a Bach cantata for the next program. At any rate, the Haydn symphony (No. 8) performed on Sunday was charming, if slight, and an interesting example of a classical piece with baroque devices still hanging on. No. 8 is part symphony, part concerto grosso, employing a harpsichord and three solo strings; the solo'cello was played with particular suavity and grace by Lawrence Lesser.

Mr. Harbison and the orchestra appeared to be most at their ease in the lively outer movements, where their energy and exuberance made an especially happy effect; the Andante seemed a bit pallid. But in the Allegro and the concluding "La Tempesta" (Haydn's cloudburst is Austrian naivete and gentility compared with Vivaldi's) they produced a sound richer and larger than the orchestra's numbers suggest. An even bigger sound could be heard in the substantial D minor piano concerto of Bach, in which the sonority of the opening unison belied the fact that the forces involved really amounted to an expanded chamber group.

Joel Sachs was the soloist, and though he was always musical his Bach seemed to me too fragile in places and too brusque in others. The employment of a Debussy pianissimo with generous use of the pedal is not always ideally suited to the baroque style. Yet Mr. Sachs showed he could play firmly and resonantly if he chose, even in mezza voce. The orchestral sections were rhythmical and well phrased.

The overture to Il Re Pastore (K. 208) by the 19-year-old-Mozart opened the program, and the orchestra played this delectable trifle crisply enough, though the same strings that were so impressive in the Bach sounded rather thin here. Even early Mozart can stand a good 25 violins. But Mr. Harbison has done good work with his players, making their attacks sharp, their rhythm excellent, and even raising the level of intonation. There is reason to expect more good things from the orchestra.