If office space were the only measure of the government's size, the federal government shrank in the past fiscal year -- by 1.048 million square feet, to be exact. That's the equivalent of a little more than 40 percent of the office space in the Pentagon.

If you added the office space that is vacant but being paid for under long-term leases, the effect would be roughly equivalent to turning out the lights and locking the door of every office in the Pentagon.

Not that any offices were actually vacated at the Pentagon. The Defense Department, along with about half of the largest federal agencies, needed more operating space last year than it had, according to statistics compiled by the General Services Administration.

The departments of Justice and Interior also gained major chunks of space in fiscal 1982, the GSA statistics show.

GSA said Interior grew primarily because of a new sub-agency, the Minerals Management Service. The Justice Department increased its space to accommodate expanded activities by the FBI and the Immigration and Naturalization Service in New York and Miami.

Space used by the judicial branch of government increased dramatically over the past year. An additional 200,000 square feet in courtrooms and judicial chambers was needed because of the 152 new circuit and district court judges authorized in the Omnibus Judgeship Act of 1978.

GSA eliminated 680,158 square feet of space nationwide, about 44 percent of the reductions in the Washington area.

The Labor Department dropped a net of 301,528 square feet, followed by the Commerce Department (down 272,346 square feet) and the Health and Human Services Department (down 270,251 square feet).

At Labor, most of the reduction was attributable to RIFs and program trims in the Employment Training Administration, according to GSA. The cuts at Commerce were largely a result of transferring the Maritime Administration to the Transportation Department.