Marvin Sadik, the director of the National Portrait Gallery for 12 of its 13 years, announced his resignation yesterday, effective July 1.

"I think 12 years is enough," said Sadik, who is 48. "I think the gallery could benefit from another person with fresh insights and energy. I really don't think I can give the job everything I've given it for 12 years. It's been my whole life."

Sadik, who is credited with having given the museum a vital image, said he has been "seriously" thinking about resigning from his $50,000-a-year post for the last six to eight months.

Sadik's father had a stroke last year and Sadik himself had surgery a little over a year ago. "I'm fine now and Dad's smoking cigars," he said, "but it's the sort of thing that gave me pause -- when one reexamines one's life." Sadik was given a six-month travel sabbatical, which he began in February. He returned three weeks ago. "I only spent three months of it. I'd made my decision." He said he plans to move to Maine and become an art consultant.

S. Dillon Ripley, secretary of the Smithsonian Institution -- which the National Portrait Gallery is part of -- said he accepted Sadik's resignation "with great regret."

"We did everything we could to try to get him to stay," said Charles Blitzer, assistant secretary for history and art at the Smithsonian.

Sadik's departure leaves the Smithsonian's two downtown museums without directors. Joshua Taylor, director of the National Museum of American Art, died a few weeks ago. The Smithsonian will have to set up search committees for both positions. "I'm reeling under the blows," said Blitzer. Harold Pfister, who was acting director of the National Portrait Gallery while Sadik was on sabbatical, will resume the job when Sadik leaves.

Sadik built the small collection of portraits to 2,000 during his tenure. He did an exhibit of portraits used for Time magazine covers, and he managed to get the enabling legislation changed to allow the Gallery to exhibit photographs. He was also caught two years ago in the emotional and political controversy surrounding attempts to move the Gilbert Stuart portraits of George and Martha Washington from Boston to Washington, a plan loudly opposed by Boston Mayor Kevin White and Sen. Edward Kennedy (D-Mass.).

"We tried to establish a standard of excellence in the way a gallery should operate and the way an exhibit should look," said Sadik. "We may have set a standard for other museums to do similar types of exhibitions -- an exhibition not only with art objects but with other related objects that help to explain it. A whole ambiance, an epoque, is suggested. It's not just a long row of pictures."

Sadik had been approached by several museums in the last few years, including the Los Angeles County Museum, which offered him the position of director about two years ago. Known for his unabashed wit, Sadik announced at one point when he was meeting with the L.A. officials, "I've met enough trustees. I want to meet some movie stars!"

Sadik, who was once the director of the Bowdoin College Museum of Art in Maine, plans to live in Falmouth Foreside, Maine, outside of Portland.

"I won't be far from Ed and Jane Muskie," said Sadik of his friend, the former secretary of state. "Maybe I could mow their lawn."