Fairfax County government, which is trying to save millions by cutting programs and delaying salary increases, is paying more than $41,000 per month to rent private office space that it no longer uses.

With one year left on the lease, the county could be required to pay more than $500,000 for the offices unless it renegotiates the agreement or finds someone to sublet the space, according to the head of the county's Office of General Services.

That amount is roughly equal to what the County Board last month agreed to spend, after acrimonious debate and fiscal soul-searching, to finance a national advertising campaign to attract new businesses to the area.

The issue of the lease for empty space comes just two weeks after Acting County Executive Richard A. King asked his staff to be ready to squeeze millions more from its agencies so the county can pay its bills through June.

"I'm very concerned and I plan to look into it," said Supervisor Sharon Bulova (D-Annandale), who chairs the board's budget subcommittee. "We can't afford to be losing money at a time when we're trying to save money out of our budget."

Although the lease involves a tiny proportion of the county's $2.32 billion budget, it highlights the current sensitivities among supervisors trying to justify spending cuts in a county accustomed to generous revenue.

Two weeks ago, Board Chairman Audrey Moore (D) declined to take a final $3,000 installment of a $24,000 pay raise over three years, saying her conscience did not permit her to take the money while the county government pared agencies and denied raises to county employees.

When told of the lease, Moore called it "a terrible waste of money at a time when it's badly needed for other things."

The county has been saddled with the empty offices in the vicinity of Dulles International Airport since Nov. 10, when it moved 208 Department of Environmental Management employees out of the 33,522 square feet of space and into the agency's headquarters at Fair Oaks near Interstate 66 and Route 50. That means the county has lost approximately $120,000 for space it is not using.

The source of the problem is the slowdown in the building industry, causing hundreds of layoffs in the department, which regulates construction. With layoffs opening extra space at its headquarters, the department moved the employees inside.

The county owes $494,171 on a lease, which expires at the end of January 1992, for two office buildings at 4500 and 4506 Daly Drive, according to Fred K. Kramer, director of the Office of General Services.

Coupled with an obligation to pay $20,000 in annual operating expenses for utilities, the county could be out more than $500,000 by next year.

Attempts at renegotiating the lease or finding a sub-leasee for the space have been unsuccessful, Kramer said. Efforts to sub-lease have included advertisements in local publications, including The Washington Post, he said.

"We've been fairly successful in the past, but we're in a very depressed market," Kramer said. "One deal fell through. We're trying to get a settlement."

A section of state law that allows the county to stop paying for the lease is an option the county does not like to use because it makes negotiations for future leases more difficult, Kramer said.

The county has structured Environmental Management so that the fees generated by building permits and inspections should enable the agency to pay for itself without county funds. But the county has had to give the department millions out of the general fund because the slowdown has made it impossible for the agency to be self-sustaining, county officials said.