SOMETIMES IN the evening, when it is dark and work is done, he slips out of the Corcoran Gallery of Art, walks across the Ellipse, and simply stands there.

"I just look at the whole building," says Peter Marzio, director of the Corcoran. "It's like this elegant lady -- you're not quite sure how old she is or what she does, or whether she's rich or poor. You can't define her. But that's part of the Corcoran tradition -- underatatement."

It seems an oddly romantic sentiment for the toughminded 36-year-old who occupies the precarious middle ground between esthetics and business. And especially so for the schlor-turned-manager who believes that "the really bright people in America are in business, not in the universities."

After 20 months in the job, "I'm almost embarrassed by how much I like the practical side," he says. And whatever self-confidence he lacked when he took the position, he has developed: "I could save Chrysler if I had to," he says, his half-smile becoming a playful taunt. Bring it on, he seems to say -- then laughs at his own response: "That's how arrogant I am."

There is a lot of the practical side to like. He runs a museum -- and school -- still scarred from its rocky financial past, manages a staff of 135 and a current annual budget of $3.7 million. In addition he contends with charges of elitism, with grumblings from the local arts community, and the challenge of turning the museum into an institution that can do almost whatever it wants to do.

And he clearly brings an air of stability. "For the first time since I've been here," says Jane Livingston, associate director, who arrived at the Corcoran in 1975 as chief curator, "I feel like the place is going to be around for another 50 years or so. Sometimes i wasn't so sure."

In the late '60s and early '70s those who ran the Corcoran racked up big deficits and went beyond spending interest to whittle down the museum's endowment principal. Over five years, the endowment -- once as large as $5 million -- was drained by about $1 million to cover deficits, according to Corcoran board president David Lloyd Kreeger. But at the same time, they began showing the riskiest of avant-garde art and found themselves on the cover of Time magazine.

Marzio gets unabashedly angry about those days. "From 1968 to 1973, it was in very bad shape," he says. "If you talk to people in town, they'll tell you it was the greatest period of the Corcoran. But you should have seen the deficits -- it was unvelievable. I'm very bitter about that period.

"People want it to be as avant-garde as it once was," he continues soberly. "I'm having to put that institution back up to the way it was before."

It wasn't until fiscal year 1974-'75 -- under the stewardship of director Roy Slade, Marzio's predecessor, and Kreeger -- that the museum began its climb back into the black. And now, Kreeger says, Marzio has "conveyed an air of confidence to the outside world. And he has insured the continuation of the Gallery's running in the black."

Marzio accepts that job with almost missionary zeal, warning ominously, "All you need is one bad year and we're right behind the eight-ball again."

The man with the mission is different in many ways from other museum directors. He didn't come from the assistant directorship of another museum; he was not born rich. And "he didn't come from a family of great collectors, which sometimes is a factor in producing good museum directors," says Daniel Boorstin, the librarian of Congress and one of Marzio's Ph.D. thesis advisers.

And yet, he was everything they wanted. It was Boorstin, formerly head of the Smithsonian's Museum of History and Technology, where Marzio was then the curator of prints, who suggested to Kreeger at a dinner party two years ago that they interview Marzio. "i said, 'Who's Peter Marzio?'" Kreeger remembers. "We had laready done an intensive search. We had interviewed directors and assistant directors and narrowed it down to three."

But Boorstin persisted. "He said, 'Just go through the motions -- just interview him,'" Kreeger recalls. And they did.

"We met with Peter at lunch and we were charmed -- completely. We thought, 'Here is our man.' He had youth, vigor, dynamism; he had done scholarly work; he was an author. With the others, it was like deja vu . You see one, two, three museum directors . . . Peter was like a breath of fresh air."

"I think, at first, because he didn't come from an art museum, there 'might' have been some reservations," said Kreeger. "But not only do museum directors like him, they respect him."

Marzio is charming in an offhanded, unstudied manner. He is handsome -- almost swarthy with dark wavy hair and direct green eyes, and always impeccably dressed. On nights of black-tie openings at the Corcoran, he looks as if he was made for his tuxedo.

He was a highly elegible bachelor until he met a woman during a lecture he was giving on museum education to George Washington University masters-degree-students. He married her last July. "It all happened rather quickly -- just wham," he says, smiling, slapping a book cover closed for emphasis. His wife, Frances, is a curriculum developer for the Prince Georges County public school system.

His father sold shoes for a living in Huntington, Long Island. Marzio went to Juniata College in Huntingdon, pa., on an atheletic fellowship, playing football as well as taking up wrestling and track. For a while he majored in geology before deciding on history for his B.A. in 1965. He spent a few summers working as a rough carpenter.

He'd never even been in an art museum before college. And now, he sayd, "I'm ruined in terms of enjoying museums. I don't see the objects. I'm looking at the lighting system."

He won a fellowship to graduate school at the University of Chicago. "I just decided you couldn't go wrong going to graduate school," he said. "And Chicago seemed like a good place. I think most of my friends were going to graduate school."

("What bothered me about the academic world," he says now, "was that there was so much pretension. People could claim they were good. In business that doesn't happen."

In 1968, he got another fellowship to work at the Smithsonian on his doctoral dissertation about the popularization of fine art in 19th-century America. His advisers were Boorstin and Joshua C. Taylor, now the director of the National Collection of Fine Arts. It took him the incredibly short period of one year ("I worked very hard"). After that, the Smithsonian's Museum of History and Technology offered him a job. "It felt right," he says. "Popularizing knowledge -- that's what museums do."

He worked on a variety of exhibits, ad spent his last four years as curator of prints. In the time between the beginning of the Smithsonian job and now, he has written four books (the latest is "The Democratic Art: An Introduction to the History of Chromolithography in America"), and numerous articles. He has one book in progress.

They asked me about the Corcoran at a good time," he says. "I didn't like the idea of having one job for the rest of my life."

In the '60s and early '70s the Corcoran directors were as eccentric as the artists. One director, in a fit of anger, punched his chief executive -- at a formal Corcoran opening. (Both resigned shortly after the incident.) Directors were beloved -- as in Walter Hopps. And they were offbeat, slightly unWashington, given to wearing Sears ties -- as in Roy Slade.

"When he was appointed director of the Corcoran," remembers Slade, whose neckties had made Marzio raise his eyebrows, "he said to me,'My God, does this mean I have to wear Sears Roebuck ties?'"

Now that Marzio has inherited that position, he is sensitive to its risks. "When people make art a closed world, it makes me sick," he says. "It makes me want to vomit. I hate that clubby world. You have to make people believe art is accessible." Both he and Livingston want to avoid turning local artists into drinking buddies and creating another sort of clubbiness. "We don't want it inbred," he says. "I think that's what hurt it in its so-called grand period. You start selecting work on a personal basis. Nothing will make artists happier in the long run than a really objective museum."

And he tries to erase any clubbiness in the eyes of the community -- although in the past, local artists, including black artists from the community, have criticized the Corcoran for just that. But to entice more people in to the Gallery and make them feel comfortable, Marzio says he has stressed more readable brochures, more text on the walls, more from the education department.

"You can lose sight of the fact that you're not just talking to artists," says Livingston, who oversees all exhibits. "I tend to be extremely intent on the subtleties of my field and lose sight of th whole picture. Peter has always said to me, 'Look, Jane, your audience has got to understand.'"

The Corcoran is also a "social engine," in Marzio's words -- no longer simply "keepers of art." Not everyone is happy with the engine's performance. "The Corcoran was a very elitist institution," says Effi Barry, the wife of Mayor Marion Barry and a member of the board of the Corcoran. "I think Peter has been a little more broad-minded in dealing with the community -- partially because Armand Hammer's donation (of funding) has made admission free."

Barry says, "There has got to be some recognition that blacks have contributed to our cultural heritage." She sees the current Senegalese modern art exhibit, prominently displayed on the Corcoran's first floor, as a step in the right direction. But she says getting it to the Corcoran was "not an easy task." Barry talked with Marzio about the exhibit after she returned from a trip to Senegal with her husband. "They didn't show a great desire to do the show. They were diplomatic, but the feeling wasn't 'Oh, yes, we must do this.'"

Marzio has said several times when questioned about the exhibit that no arm-twisting was necessary. "We already had the catalogues for the show," he says. "We knew what it was."

Marzio may never satisfy the whole community. "There are people who want the Corcoran to be like a halfway house," he says. "Like what Jane Adams did in Chicago with those marvelous ethnic art exhibits at Hull House. We can't do that. That's not a function of a museum. Oh , you can have ethnic art exhibits -- but there are a lot of cultural drives where identity and not art is the main goal. That's fine, but not in a museum with the higheset esthetic standards."

Marzio is the new arrival in an art-museum hierarchy that includes such notables as National Collection of Fine Art's Joshua Taylor and the National Gallery's J. Carter Brown. Marzio and Brown both dismiss rumors of bad feeling between them because the Corcoran, instead of the National Gallery, will show a collection of paintings this year owned by Armand Hammer. "It's just not true -- not true," says Marzio. "That kind of thing bothers me. Armand Hammer is a trustee anyway."

Marzio makes his way carefully into the group, more respectful than rivalrous, yet still ambitious for his museum. He speaks glowingly of the other institutions, but takes a critic to task for saying "another museum" in the city has the best American collection. "He was dead wrong -- dead wrong," says Marzio, smiling. "We do. There are bigger collections, but we have all the punctuation marks. Here, we have the greatest luminist painting of all -- Frederick Church's Niagra Falls.'" And in photography, he adds, "We one of the leaders in the country."

In the Corcoran's future, Marzio sees a balance of projects, continuing with much regional art ("No question we'll be making a lot of noise there.") As for contemporary art -- "It's hard to say we'll make a big statement. It's not our fault. It's the state of the art."

"You know what I think the irony of all this is?" he says, his face lighting up. "From 1965 to 1978, I spent most of my time studying 19th-century political democracy and the aristocratic fine arts. The question is how those two groups came together. Much of that was done by museums. I'm like those people I studied."

He grins. "I get a kick out of that."