The Bach Society Orchestra has played some ambitious programs this year. Saturday's may well be their most difficult. The Faure Pelleas et Melisande suite is not easy; nor is Stravinsky's Orpheus. Having picked a vacation weekend to perform, the Bach Soc may well have dug its own hole. Still, Saturday night will be a good chance to hear non-warhorse material in a distinctly relaxed atmosphere.

Throughout the year, the Museum of Fine Arts in Boston produces an impressive array of chamber concerts. On Tuesday the 10th, baroque flutist Carol Epple will lead a program at the Museum. She is a very good player and can prove that ancient instruments do not have to be played out of tune. Incidentally, admission to the Museum is free on Tuesdays from 5 until 9: a good chance to look around before hearing the concert.

SYMPHONY HALL. Handel and Haydn Society. Bach: St. John Passion. Tickets: 266-1492. March 30, 8:30 p.m.

SANDERS THEATER. Bach Society Orchestra. Faure and Stravinsky. Tickets sold at the door. March 31, 8:30 p.m.

WELLESLEY COLLEGE. Slater Center. Claude Akive, voice and guitar. Chansons of Germany, France, England, Spain and Italy. April 3, 8:00 p.m.

SYMPHONY HALL. Lorin Maazel conducting the BSO. Prokofiev: Third-Piano Concerto (Israela Margalet, soloist); Sibelius: Second Symphony. Tickets: 266-1492. April 3, 8:30 p.m.

MUSEUM OF FINE ARTS. Chamber music for baroque flute, baroque oboe, and harpsichord. April 10, 7:00 p.m.