ONE OF THE MOST difficult tests of a good orchestra and its conductor is the accompaniment of a virtuoso soloist in a concerto. The weaknesses of the group are too often highlighted by playing with an outstanding musician, and its sloppy playing can detract from the best solo instrumentalist's performance.

But the Bach Society Orchestra met that test in its first concert of the season giving Yo-Yo Ma '76 the backing he deserved during a performance of the first cello concerto by Shostakovich. Under the baton of Neal Stulberg '76, this year's conductor, the potentially fragmented composition jelled into a continuous musical statement. The orchestra nimbly bridged the dangerous gaps between the cello passages and those sections played by the group; instead of pouncing on its entrances and destroying the soft, quiet effect produced by Ma in the second movement, the orchestra picked up where he left off and matched its guest's sensitivity and finesse.

The concert opened with the Overture to Mozart's opera Idomeneo. Although some inaccurate tuning and rickety entrances marred the performance of the rarely-heard work, the conductor and the orchestra paid careful attention to the shadings and contrasts in volume that contribute to the shaping of the work.

WITH THE SAME concern for drawing out the contrasts between different sections of a piece, the Bach Society turned to Beethoven's Symphony No. 1. The Orchestra followed whispering passages with resounding responses--a favorite juxtaposition of the composer. Written while its creator was under the influence of classical masters Mozart and Haydn, the symphony contains hints of Beethoven's spirit of adventure in the final two movements. Stulberg conducted the repetitive and less interesting first half of the piece too slowly, adding, however, to the effect of the lively third and fourth movements which the orchestra performed with extra zest.

Moving ahead about a century in musical literature, the orchestra turned to Bela Bartok's Rumanian Dances. Fascinated by the folk music of eastern Europe, the composer combed the countryside of Hungary, Rumania and Slovakia recording the songs he heard. Not content with imitating the melodies in his own music, Bartok, as he once wrote, tried to "command this musical language so completely that it becomes the natural expression of his own musical ideas." The Bach Society responded to the unique harmonies and rhythmic patterns and conveyed well the vitality Bartok found in the Rumanian villages.

Throughout the concert Stulberg conducted with authority and a precision matched by the performance of the orchestra. Never overstating his movements, Stulberg achieved what he wanted by subtle proddings of the baton. The orchestra played better than it has in the last several years, and this at only the start of their season. If the Bach Society improves over the year, as it usually does, we should be hearing some superb music.