The Fairfax County Board of Supervisors approved a master plan change last night designed to clear the way for a major employment, residental and office complex at the intersection of the Capital Beltway and Rte. 50.

The proposed $250 million development-- which still needs rezoning approval from the supervisors -- would create about 7,000 jobs and generate about $5 million in annual tax and other revenuesfor the county, according to the developer, Cadillac Fairview, a Canadian real estate firm.

The project was vehemently opposed by some residents of the area around the interchange who objected at a publichearing that traffic and flooding problems would worsen.

Board members expressed satisfaction last night with Cadillac Fairview's proposal to spend $12 million on highwayimprovements for access to the 178-acre site in the southeast quadrant of the interchange. Those improvements would include ramps to enable traffic to move from the beltway's southbound lane directly to Rte. 50 headed east.Motorists now must take a more circuitous route.

The master plan amendment, approved on a 6-to-3 vote, also was drafted in an effort to meet the objections of the tract's neighbors. It sets the maximum height of residential construction at three stories rather than the six the developers wanted.

Supervisor James Scott (D-Providence) proposed setting maximum limit of nonresidential development at 2 million square feet, a quarter of a million square feet below the developer's compromise request. The proposal was rejected, with the board approving the 2.25 million square feet the developers had asked for.

To protect the Holmes Run stream flood plain, which bisects the tract the master plan was changed to require the developer to provide for disposal of any storm water runoff that exceeds predevelopment levels.

The board also adopted a 35 percent open space requirement west of Holmes Run, further restricting the developer.

David Weinberg, senior planner for Cadillac Fairview, said, "I'm prepared to live with it although it is more than double the requirement for this type of zoning. He said his company also would have problems with the three-story limitation. "It means we can't have condominiums," he said.

The complex that Cadillac Fairview wants to build would have a 350-room hotel, 650 housing units, including townhouses, 1-9 million square feet of office space and 50,000 square feet for retail stores.

The board agreed last night to coordinate development of the southeast and north east quadrants of the interchange and placed a ceiling of 3.6 million square feet for nonresidential development for the two sites combined.

Weinberg said his company and Costain Ltd., the contract purchaser of the northeast quadrant, are negotiating overoffice space allotments.

The board's decision to accede to the developer's request for 2.25 million feet of nonresidential construction was influenced by the fear that the firm would withdraw its proposal.

In a letter to Scott yesterday, Martin Walsh, the developer's attorney, said the company had already reduced itsrequest for 3 million square feet of nonresidential use and would like to seethe ceiling go below 2.25 million.

Arguing for that ceiling last night, Supervisor Marie Travesky (R-Springfield) said, "If we . . . adopt this with 2 million we may be dooming this to failure . . . Very few people have the money to see this through to a satisfactory conclusion."

The location for the proposed development -- called the Chiles tract -- had been described as among the choicestundeveloped sites in the Washington area because of its position at the intersection of major highways.

A major rezoning battle may still be in prospect for the Cadillac Fairview project. Kevin Bell, president of theRaymondale Civic Association, said last night that "if both the northeast and southeast (quadrants) are considered together, i think the citizens in the area will be able to show to the board that the development asked for is too large."

Voting for the master plan change last night were supervisors Traversky, Martha V. Pennino (D-Centreville), Joseph Alexander (D-Lee), Sandra L. Duckworth (d-Mt. Vernon),Nancy K. Flack (R-Dranesville) and Board Chairman F. Herrity (R). Voting against were Scott, Thomas M. Davis iii (R-Mason) and Audrey Moore (D-Annandale).