The Fairfax County Board of Supervisors approved rezoning last night for a $325 million development in the area just west of Fair Oaks Mall after securing from the builders a promise of a $5 million contribution toward construction of a $7.8 million highway interchange.

The Centennial Gateway project will be about one-fourth the size of the present Tysons Corner development and will include a 350-room hotel, three man-made lakes, apartments, townhouses, a shopping center and substantial office space on 80 acres.

The land rezoned unanimously yesterday by the board is a wooded area just west of Fair Oaks Mall, straddling West Ox Road, along the south side of Rte. 50.

Centennial Gateway is contributing $5 million to the cost of an interchange incorporating a bridge, designed to help relieve congestion at the already traffic-choked intersection of West Ox Road and Rte. 50.

"I think it's good," said Supervisor Audrey Moore, who supported the rezoning, but who has in the past been critical of her board colleagues for not seeking enough money from developers for the road improvements necessary to support their own developments.

Moore called the development "beautiful."

Design of the interchange is required to be complete within a year, and officials predicted construction might be complete within two.

County officials said that, along with the contributions from other developers in the so-called 50/66 development area, the county's contribution to cost of building the interchange should be relatively small, and may end up being only a loan.

Centennial Gateway is set to be built in stages over 11 years, and so far only three office buildings have been specifically approved.

Centennial Gateway officials said that groundbreaking ceremonies on the first building probably will be held this fall.

County board members praised the work of Supervisor James M. Scott, in whose Providence district the development lies.

Scott mediated at 47 meetings over 15 months between developers and community members, persuading Centennial Gateway officials to modify the original development proposal significantly.