"Charlie and Algernon" opened Sunday night at New York's Helen Hayes Theater to a standing ovation -- a routine event for the show since it first played the Kennedy Center last March -- and to disappointing reviews.

At a meeting of the co-producers yesterday afternoon, Kennedy Center chairman Roger L. Stevens, Folger Theatre Group producer Louis Scheeder and their associates decided to keep the show open through this week at least, despite a meager advance sale. After that, "We may see what happens when a good word-of-mouth show has to face the challenge," said Michael Sheehan, the Folger's associate producer.

The musicial stars P. J. Benjamin and Sandy Faison, and has a book and lyrics by David Rogers and music by Charles Strouse. Earlier versions of the Rogers/Strouse adaptation were produced in Edmonton, Alberta and London.

The Folger Theatre Group first mounted its production at the Terrance Theater in the spring, and then brought a somewhat larger pre-Broadway edition back to the Eisenhower last month. During two weeks of New York previews, "the audience reaction was literally just as good as it was in Washington," Sheehan said yesterday. He and Scheeder are remaining in New York to follow developments. The co-producers aren't sure the show can survive the bad notices, Sheehan said, "but we're sure going to try."