Jean-Claude van Itallie, a playwright, director and performer who was a mainstay of the experimental theater world and who was especially known for “America Hurrah,” a form-bending trio of one-acts that opened in 1966 in the East Village and ran for more than 630 performances, died on Sept. 9 in Manhattan. He was 85. His brother, Michael, said the cause was pneumonia. Beginning in the late 1950s, Mr. van Itallie immersed himself in the vibrant Off Off Broadway scene, where playwrights and performers were challenging theatrical conventions. He joined Joseph Chaikin’s newly formed Open Theater in 1963, and his first produced play, “War,” was staged in the West Village. He was a favorite of Ellen Stewart, who had founded La MaMa Experimental Theater Club in 1961.