The federal government has launched an "aggressive" campaign to secure commercial office and retail tenants for unneeded space it leases or owns in Washington-area buildings.

A declining work force at many federal agencies has left small blocks of unused space in scores of buildings. Rather than continuing to pay a required "rental fee" to the government for vacant space, the agencies are turning it back to the General Services Administration -- the government's housekeeping agency -- for disposal.

Throughout the metropolitan area, there are more than 2 million square feet of vacant space -- about twice the usual inventory, GSA said -- out of a total of about 29.7 million square feet of leased space.

GSA estimates that it will earn from $1.5 million to $3 million in what it calls "outleasing" in fiscal 1983. Its 2 million square feet of unneeded space in the region is estimated to be worth $18 million.

"This program is one of the major public building service initiatives this year," said GSA's Public Buildings Commissioner Richard O. Haase. "We will be monitoring these activities closely and certainly the National Capital Region is showing results from its aggressive marketing activites."

After trying to find other federal tenants -- such as the Defense Department, which is expanding -- GSA tries, in the case of leased space, to return it to the building owners. GSA officials say they are often unsuccessful and have now embarked on an aggressive campaign, which includes tear-out-coupon advertising in newspapers, to let the space to small offices and retail establishments.

The effort got off to a rough start in September when GSA did not receive any acceptable bids on the first three properties it offered -- one of them at 711 14th St. NW, just a block from the city's red-light strip of pornographic movie theaters and bookstores.

But this week, GSA announced it had succeeded in leasing two properties.

* Federal Data Corp. will expand its offices by taking over 4,000 square feet of government-leased office space in the One Park North Building, at 5550 Friendship Blvd. in Chevy Chase. GSA will earn $65,240 a year, just under the $68,000 it made in rent from the Justice Department. Another 4,000 square feet is still available in the building.

* Georgetown University's National Center for Education in Maternal and Child Health will occupy 3,000 square feet of office space at the Old Streetcar Barn at 3600 M St. NW. The space was previously used by the Drug Enforcement Administration. Georgetown will pay $27,000 a year, less than DEA's annual tab of $33,000 for the space. GSA is still trying to find someone to lease DEA's adjacent pistol firing range as warehouse space.

Next on GSA's agenda is leasing about 150,000 square feet of space at a dozen locations. Major properties include:

* 27,289 square feet of what the GSA calls "plush office space" at 5225 Wisconsin Ave. NW, previously used by the National Science Foundation.

* 15,000 square feet of space at the Center Buiding Number One, 6505 Belcrest Road, Hyattsville, which was previously used by the Agriculture Department as laboratory space. GSA said it is looking to lease it either as lab space or as office space.

* 7,000 square feet of space at the Bicentennial Building, 600 E St. NW.

* 5,000 square feet of space at the Vanguard Building, 1111 20th St. NW.

* 2,218 square feet of space at the Board of Trade Building, 1129 20th St. NW.

GSA real estate specialist Ken Perrin said the agency's newspaper coupon drew nearly 60 responses from individuals interested in leasing vacant government space, some of which the agency did not even know was available.

"This program is helping the government to manage its space more efficiently, because the interest from the private sector [in space we advertise] is helping us negotiate our way out of leases with landlords," Perrin said, indicating that the government would rather not be in the subletting business.

For example, the 14th Street property that GSA unsuccessfully tried to sublet won't go back on the market because K&K Properties, the building's California-based owner, is now interested in taking it off of the government's hands.

Most of the outleasing will be in space rented from the private sector, but in certain instances federally owned space not considered suitable for government use will be leased. GSA said its intent is to relocate agencies from leased to federally-owned space whenever possible. For example, GSA recently leased 849 square feet of retail space at the Lafayette Building, 820 15th St. NW, to Stern Shoe Repair. That ground-floor space, in a government-owned building, had previously been used by a dress shop, which went out of business.