Leon Fleisher will not play the piano, as originally scheduled, in two concerts by the Theater Chamber Players next weekend at the Kennedy Center. His place will be taken, in Mozart's Quintet in E flat for piano and winds, by Dina Koston, cofounder of the chamber ensemble.

The concerts would have been Fleisher's first appearance in standard repertoire since his dramatic performance with the Baltimore Symphony Orchestra last year for the inauguration of the new Joseph Meyerhoff Symphony Hall.

Fleisher's right hand was disabled in the mid-1960s by a crippling illness related to writer's cramp, for which he is still receiving therapy. His rehabilitation "is progressing," he said, but "the whole rate of restrengthening and progress has not been as fast as the doctors and I had hoped. The Mozart, when you go for a certain kind of sound, is very difficult. The control is not there constantly to my satisfaction."

Despite the cancellation, Fleisher said he is confident he will be able to resume a limited schedule of concerts with orchestras next fall. Columbia Artists' management, he said, "has arranged a small handful of orchestra dates for me, which I have every hope of fulfilling starting in September."

Possible repertoire will include the Franck Symphonic Variations, Beethoven's Second Concerto and Brahms' First. He also plans to perform with Koston for the Theater Chamber Players at Kennedy Center in Brahms' "Liebeslieder" waltzes, which require two pianists.

He will be taking a sabbatical from his teaching duties at the Peabody Conservatory in Baltimore and the University of Michigan, as well as from conducting engagements. He has accepted about nine piano engagements for next season, including one with the New York Philharmonic in May 1984, probably for three or four performances.

"The doctor says it should be possible for me to play every three or four weeks," he said. "I don't know whether I will ever accelerate beyond that, but I can't see myself ever doing two or three concerts per week and going through the year. That's impossible, not because of physical stamina but because of the feeling of mass production it engenders."