Stephen J. Richard, managing director of the Pittsburgh Ballet Theatre, will become executive director of Arena Stage in February, Producing Director Zelda Fichandler announced yesterday.

Richard, 39, takes over a position left vacant since the September 1989 resignation of William Stewart, who left after a season in which earnings were not as high as expected. During the past year Associate Producer Guy Berquist has assumed many of Stewart's responsibilities, in conjunction with a management team made up of board members and department heads. That team also recommended changes in the management structure od the theater, which has an annual budget of about $10 million and is facing the departure of cofounder Fichandler next spring.

Richard will become part of a new management triumverate, along with Berquist, who has been given the new title of general manager, and Douglas C. Wager, who is to replace Fichandler as artistic director. Fichandler is leaving to be artistic director of the Acting Company in New York and to continue teaching at New York University's Tisch School of the Arts.

"The transition from Zelda to Doug is going to be extremely interesting," said Richard. "Frankly I don't know of a theater in the country who has handled that sort of thing well. But Arena is a trendsetter, the theater that others look to to be the model."

"Stephen Richard has precisely the right qualifications, interests and personality for the job," Fichandler said in a press release issued yesterday.

Before joining the Pittsburgh Ballet Theatre in 1987, Richard spent seven years at the Los Angeles Theatre Center, which had a $16 million budget when he left. He has taught arts management at California State University, Los Angeles, and at Carnegie Mellon, and is national co-chairman of the Managers Council of Dance U.S.A. He is a graduate of Reed College with an MA in American history from UCLA.

Stewart and Fichandler divided the artistic and management responsibilities, although Fichandler was final arbiter of all decisions. Wager, Berquist and Richard will have equal authority, with Wager handling such artistic decisions as play and director choices, Berquist managing the day-to-day operation and the production schedule, and Richard focusing on fund-raising and long-range planning.

"Arena is about to discover what's next," Richard said. "I think that's going to be extremely interesting."