Mikhail Baryshnikov will undergo arthroscopic knee surgery in New York next Tuesday, a spokesman for American Ballet Theatre, Baryshnikov's company, said last night.

As a consequence, he will be unable to perform at Wolf Trap, where he was scheduled to dance three performances during ABT's engagement there August 26-31. He will also miss the company's "encore" season at the Metropolitan Opera in New York, Sept. 3-15, for which he was slated for six performances, including a Sept. 4 "Romeo and Juliet" gala. Baryshnikov is artistic director of the company.

The surgery will be on the right knee, which was operated on in 1983 in Chicago; it has given him periodic trouble ever since. Baryshnikov, 37, hurt his knee again in a dance class in Cleveland last Wednesday while on a strenuous 29-city tour with his own small summer traveling troupe, Baryshnikov and Company. He flew to New York the next day to consult with his doctor, William Hamilton, an orthopedic specialist who will perform the surgery. At that time, the doctor advised Baryshnikov to wait and see. After his final performance with the touring troupe in Springfield, Mass., Monday evening, however, the knee had worsened and Baryshnikov decided on the surgery after another consultation with Hamilton.

The ABT spokesman said it wasn't known yet how long Baryshnikov would be incapacitated, but that he would continue directing ABT and might be able to return to dancing in time for the company's national tour next year.

"White Nights," a movie costarring Baryshnikov and Gregory Hines, is set for Christmas release.