The Fairfax County Board of Supervisors approved a $400 million proposal yesterday to build a downtown for mostly rural Centreville, peacefully capping more than a year of intense negotiations between the developer and citizens groups.

With the board's 6-to-0 vote, the project's primary developer, Cadillac-Fairview Co., will build a 125-acre complex called Trinity Centre, which residents and county officials hope will provide a focal point and an identity for one of the county's last largely undeveloped areas.

"We have now a development they {residents} can live with very well and something they can be proud of," said Supervisor Elaine McConnell (R-Springfield).

The Cadillac-Fairview project is one of several developments planned for the Centreville area. Together, the projects could generate more than 6,000 residential units and several million square feet of office, retail and hotel space in the next 20 years, planners said.

The Trinity Centre complex is to include nine office buildings with a maximum height of 10 stories, a 300-room hotel, 764 garden apartments, a movie theater, an outdoor entertainment area and a three-acre lake with surrounding pathways.

The plan has undergone a number of incarnations since citizens groups learned of it more than a year and a half ago and mounted a battle against it.

For example, the project has been reduced by about 500,000 square feet of office space, and the maximum height of the office buildings has been reduced from 16 stories to 10. About $17.5 million in road improvements are being offered by the developer.

"We're very pleased," said John Litzenberger, president of the West Fairfax County Citizens Association, a coalition of 20 homeowner and civic associations. During a brief hearing yesterday afternoon, Litzenberger was one of two speakers who urged the board to rezone the property from a commercial district zoned for a regional shopping center to a planned development commercial district.

The county planning staff recently recommended rejection of the project because of concerns that more road improvements were needed, but the staff later reversed its position after the developer offered some concessions.

Among its major concessions, Cadillac-Fairview offers to provide for the design of the interchange at Rtes. 28 and 29 and promises to phase in the construction of no more than half of the project over the next six years.

Ten percent of the 764 apartments will be reserved for low- and moderate-income families.

In other actions, the board:Voted 5 to 0 to rezone a tract near the future Reston Town Center to permit construction of a 30-unit rental town house complex for low- and moderate-income families.

The $2.1 million project, which drew 26 residents to the board meeting in support, will bring to 96 the number of public housing units available in Reston, a planned community in western Fairfax.

The three-bedroom town houses, costing about $71,000 each, would be built with federal funds on 2.9 acres donated by the Reston Land Corp., the developer of Reston, at the northeast corner of Town Center Parkway and Bowman Towne Drive. Denied a request by developers Alan I. Kay and Samir Kawar that the county give them density credit for having donated land near Dulles International Airport for the Center for Innovative Technology headquarters. The developers had hoped that in exchange for the land, they would be allowed to build offices on adjacent land that is slated for residential uses in the county's comprehensive land use plan. Voted 5 to 0 to rezone a 37-acre tract immediately west of the Fair Lakes office park and merge it with the 620-acre development.

The tract was zoned for one house per acre, and the Fair Lakes developer, Hazel/Peterson Co., wanted about 408,000 square feet of development at a 2-to-1 ratio of commercial to residential. The rezoning would increase the maximum commercial space allowed at Fair Lakes from 5,078,000 to 5,350,200 square feet and increase the minimum number of dwelling units required in the development from 1,321 to 1,457.Staff writer John Ward Anderson contributed to this report.