For a violinist or cellist the ultimate challenge is the Bach solo literature because, quite simply, Bach demands the impossible, particularly in the case of the violin. One player must do the work of several, creating with a single line the illusion of two, three, even four voices sounding separately.

On Sunday afternoon in the final round of the 20th Bach International Competition the challenge of playing Bach for three days was clearly visible on the pale, perspiring faces of the competitors. Fortunately for them, they could not be seen by the judges, who were isolated behind a screen to one side of the stage, part of a rigorous procedure that attempts to guarantee that judgments will be made only by ear.

Perhaps because their task was, if by the smallest degree only, more demanding, the violinists showed more strain than the cellists. According to Raissa Tselentis, founder and director of the competition, violinist Timothy Baker, first-prize winner, said to her just before his turn, "I'm not coming out. My fingers ache." Tselentis, of course, sent him out anyway.

Although fairness is strived for, no competition can control the audience. The big popular favorite from all the finalists was second-prize winner, for violins, Dmitry Sitkovetsky, a recent immigrant from Moscow. Giving the same kind of passionate performance as his fellow countryman, Mstislav Rostropovich, frequently does, Sitkovetsky was cheered and applauded enthusiastically by the audience, which could be observed by the judges.

Apparently uninfluenced, judges Miran Kojian, George Donderer of Berlin and Rafael Druian tended to favor maturity and subtlety over drama and emotion in performance. Unrelenting, the crowd vociferously cheered its Russian favorite once more when the prizes were announced.

For violinists the winners were Timothy Baker, a student of Nathan Milstein, first: Dmitry Sitkoversky pupil of Ivan Galamian, second; and Cecylia Arzewski, a pupil of Galamian and Joseph Silverstein, third.

Charles Curtis, an 18-year-old from Los Angeles, won first for cellists: Nancy Green, a pupil of Leonard Rose and Carl Schachten, took second; David Finckel, a Rostropovich pupil, took third; and Daniel McIntosh received honorable mention. First-place winners received $1,500, second place $500, and third $250.