The National Rifle Association has decided to move 400 of its employees from the District to a new building in the Fair Oaks section of Fairfax County, Board of Supervisors Chairman Thomas M. Davis III said.

"It is an indication that the county's pro-business policies are paying off," he said. "We are extremely pleased that they decided to locate here."

Officials at the NRA declined to comment before the Fairfax Weekly's Tuesday afternoon deadline.

The move, which had been under discussion for several months, initially was held up by county officials' concerns about moving the NRA's basement firing range to the new building.

Davis said the association has now received all the necessary approvals from the county for the underground range.

The NRA will buy the Summit 66 office building at 11250 Waples Mill Rd., Davis said.

Among the NRA employees who will be moving to the building are firearm coaches, training safety instructors and researchers. The NRA's political division will remain at 1600 Rhode Island Ave. NW, Davis said.

Supervisor Katherine K. Hanley, who represents the Fair Oaks area, said she was glad the NRA has decided to move to Fairfax.

"As you know, I don't have to agree with somebody's politics to be happy that they are a tenant in the Providence District," she said.

Fairfax County has long been trying to lure businesses and associations away from the high-priced real estate of downtown Washington.

In the last year, several companies have moved large parts of their operations to the county, or have announced their intention to do so.

American Management Systems has moved 900 employees from its headquarters in Arlington to Fair Oaks. American Mobile Satellite Corp. has moved its headquarters from the District to Reston, and plans to employ 600 people there by 1995. The management consulting firm of Booze-Allen & Hamilton consolidated about 1,000 workers from Arlington and Montgomery in their new headquarters in Tysons Corner.

Davis, who was elected on a pro-business platform, has led efforts to fill Fairfax office space with businesses from Maryland, the District and other parts of Virginia.