The Corcoran Gallery of Art, in an effort to avoid a budget deficit, is cutting its museum staff by nearly 15 percent.

Peter C. Marzio, the Gallery's director, yesterday informed his staff that seven jobs are being abolished. There are about 50 employes on the museum's staff. Five of them -- one each in the museum's shop, in the development office, in building maintenance, in special events and in the registrar's office -- have been let go, he said. Two additional positions, both of them now open -- one a preparator's job, the other a post in the finance office -- will remain unfilled. Overtime guard pay also will be reduced, Marzio said.

"Hiring is hard. Firing is harder. It is an awful thing to do," he said. "All the people we are letting go are good people. They were doing a good job. But we are not going to start the fiscal year -- it begins September 1 -- with a predicted budget deficit. We have to live within our income.

"The Corcoran raised more money -- some $3.5 million -- in fiscal 1982 than it ever had before," he said. "And we came in right on budget. We plan to spend almost exactly as much next year. But we expect to take in less."

Marzio said the job cuts are expected to save the gallery approximately $150,000.

Marzio, who is leaving the museum on Oct. 1 to become director of the Houston Museum of Fine Arts, said declining interest rates will lower the Corcoran's endowment income in fiscal 1983. The continuing recession, he added, is expected to diminish grants and outright gifts.

"Sales in the shop also are down a bit, and we're finding fewer dollars in the collection box by the door," he said. "It's no good making believe it's not happening. We tried that in the early '70s, when we ran up huge deficits. We're not going to do that again. We've been operating in the black. We're going to stay in the black. Big corporations and foundations will not give to an institution that does not have a balanced budget."

Since Marzio joined the Corcoran in 1977, its financial health has improved steadily. Though admission charges have been abolished, annual income is up by nearly $1 million. Annual attendance has increased more than fivefold, from 85,000 to 500,000. And the museum is now air-conditioned. Its new climate-control system cost $1.95 million, of which $1.65 million already is in hand, said Marzio.

A number of museum staffers attribute the staff cuts, at least in part, to Marzio's departure. "The trustees are being cautious, and no wonder," said one employe. "Peter proved he could raise money. Whether his replacement can bring the cash in remains to be seen." A new director for the Corcoran has not yet been selected.

Marzio said the Corcoran's trustees "will meet in January to reexamine the situation. If the situation brightens, we'll start hiring again."