The Fairfax County Board of Supervisors has approved construction of a $75 million mixed-use office and apartment development in the Fairfax Center area.

The project, which will include two 11-story office buildings and two apartment buildings, will be built by West Ox Development Corp. and a joint venture partner to be announced later. West Ox Development is associated with the McLean-based Julien J. Studley Inc. real estate operation.

The mixture of office and residential use complies with Fairfax County's land development plan for the Fairfax Center area near the I-66 and Route 50 corridor.

"The plan meets all the criteria for a PDC planned development commercial development in Fairfax Center. It has a mix, a variety of housing and commercial space included," according to project attorney Barnes Lawson.

Construction is slated to begin in early 1986, said Paul Schweitzer, president of West Ox Development Corp.

"The two 11-story office buildings containing 425,000 square feet of office space will be connected by a landscape plaza," Schweitzer said.

The apartment buildings, containing a total of 180 units, will be terrace structures providing balconies for many of the apartments, Schweitzer said. He said the project will be situated on one of the highest points in that part of Fairfax County.

The residential units are "a strong part of the total development. It is more urban in nature" than other multifamily projects proposed in the area, he said. The units likely will be rented "to young professionals" who will be working in the rapidly growing Fairfax Center area.

In a departure from traditional planning for mixed-use development in Fairfax, the builder is using two architectural firms. Skidmore, Owings & Merrill of Washington designed the commercial buildings; CHK Architects and Planners, with offices in Washington and Arlington, designed the residential buildings.

"Our site has the best access of any project" in the Fairfax Center area, Schweitzer said. "We are providing a new Legato Road through to West Ox Road."

Developers must contribute more than $1.3 million to the county's fund to provide for future road improvements in the Fairfax Center area. Contributions required of developers in that area are calculated on the basis of square footage of commercial or office space and at $600 per residential unit, Lawson explained.

The site is on the west side of Legato Road, south and east of West Ox Road. Fair Oaks shopping mall is immediately west of the development.

"This property is located in the proposed 'mixed-use village core' of the Fairfax Center area. Most of the surrounding property is planned for a mix of office and high-density residential uses," according to the county planning staff.

Developers agreed to more than a dozen proffers, or promises, dealing with land use, transportation and environmental issues before winning unanimous support by the board for the project. The original zoning was filed in June 1984.

The developers agreed to help pay for traffic lights at West Ox Road and Legato Road, to dedicate and pay for widening portions of West Ox Road and to provide pedestrian access along the southern edge of the site.

Fairfax is requiring the developer to coordinate landscaping along West Ox Road with Centennial Development Corp.'s giant Centennial Gateway mixed-use project, which has been approved for construction west of the site.

A swimming pool, tennis courts and picnic areas are part of the development plans approved by Fairfax.

More than 32 percent of the total 13.9-acre site will be left in open space, according to planning officials.