Jean Firstenberg, a program officer with a New York educational charity, has been named to succeed George Stevens Jr. as director of the American Film Institute.

Stevens and actor Charlton Heston, chairman of the AFI board of trustees, made the announcement yesterday at a press conference in the AFI screening room at the Kennedy Center.

Firstenberg, 43, a media project planner and admistrator at the John and Mary R. Markle Foundation, will assume her new post on Jan. 2.

Firstenberg said yesterday, "It is time to develop a 10-year plan to strenghthen existing programs and find ways to grow in new areas." She said that she foresees the AFI "standing alongside the Smithsonian Institution, the National Gallery of Art and other major cultural institutions in the decades ahead."

Firstenberg said she would devote the first several weeks of her three-year appointment (at an annual salary of $62,500) to a thorough evaluation of the AFI's activites, before determining priorities. Speaking on behalf of the board, Heston took the opportunity to reaffirm commitments to film education and archival programs, including the massive, unfinished reference project designed to catalog American film production since 1893. "We've gotta find the money to finish it," Heston declared.

Firstenberg is the daughter of Eugene Picker, a former president of Loew's Theaters and one of the country's most respected exhibitors. David Picker, the former head of production at United Artists and now an indepndent producer, is her older brother. David Picker was also a recent member of the AFI board of trustees, but according to Stevens, he played no role in the process that led to his sister's selection as director. "She came in on her own merits and simply won the job," Stevens said.

The new director graduated summa cum laude from Boston University's School of Public Relations and Communications. She has worked as director of the university's FM radio station, assistant to the president of WMGM-AM in New York City and as an assistant producer of public affairs television shows at WRC-TV in Washington and an advertising executive at J. Water Thompson. She later served as directed of the publications office at Princeton University.

While at the Markle Foundation, she was instrumental in encouraging and then helping fund the AFI's Directing Workshop for Women, located at the Center for Advanced Film Studies in Los Angeles.Stevens worked with her briefly in 1965 when he was director of the United States Information Agency, and Firstenberg had helped organize American participation in the Moscow Film Festival.

In introducing Firstenberg, Stevens said that "it became clear that we had to find a rather unique person" who would be "comfortable in the world of Washington, from which a sizable portion of our funding comes, and also in the worlds of education, independent film and video production and the creative and business world of the motion picture and television industry. It's difficult to find someone who can travel easily between these worlds, but, happily, our board has achieved that."

Heston said Firstenberg was the "unanimous recommendation" to the full board of a 10-member search committee that spent about five months narrowing a preliminary list of 60 candidates down to 10 finalists.

Stevens had adked the AFI board to seek a new director last summer, in order to devote more of his time to independent producing ventures. He has agreed to remain with the AFI as co-chairman of the board with Heston.

Firstenberg will move to Washington in the next few weeks. Stevens to me," while "spending some time in California" on unspecified projects. He will continue as the producer of the television specials devoted to the AFI's annual Life Achievement Award and the Kennedy Center Horors. CAPTION:

Picture, Jean Firstenberg, by Harry Maltchayan