The Fairfax County Board of Supervisors has deferred until next week a decision that would clear the way for construction of a major employment, residential and hotel complex at Rte. 50 and the Beltway.

Cadillac Fairview, a Canadian real estate firm, has proposed a $250 million project that would include a 500-room luxurey hotel, offices and 550 townhouses and condominiums. The complex would be on 178 acres of land known as the Chiles tract, at the southeast corner of Rte. 50 and the Beltway.

Before the Cadillac Fairview proposal could be considered, the supervisors would have to amend the county's masterplan for the area.

Nearby residents told supervisors a board meeting Monday changing the master plan to permit development of a major employment center would have adverse effects on their neighborhoods.

"Six-story buildings will cast shadows in our backyards," said Kate Hanley, president of the Holmes Run Woods and Crossing Civic Association. "It will be our steets where workers, if there is not sufficient parking in the development, will park and walk through the buffer to work. Lights that are too high will shine in our bedrooms."

Although the residents said they would prefer that the tract remain as wooded parkland, they told the board that in six months of meeting with Cadillac Fairview planners, they have "moved a long way" toward acceptance of the developers' proposal.

Opposition to the proposed master-plan amendment centers around the county's ability to control the traffic and flooding problems, which residents contend would develop if the complex is built.

Cadillac Fairview estimates the project would add $5 million annually to county revenues and would create 7,000 jobs.

In its report to the board, the Providence District Task Force, which evaluated the proposed master-plan change, complained about a county planning staff recommendation for urgency in adopting the change.

"The task force takes exception to the statement that consideration of this item is urgent because there is a pending rezoning application," the report reads. "This justification is clearly a bootstrap argument."

To satisfy complaints about traffic at Rte. 50-Beltway intersection, which already is congested at peak hours, Cadillac Fairview has proposed spending $12 million on highway improvements, including constructin of ramps from the Beltway to allow for a more direct route from southbound lanes of the Beltway to eastbound lanes of Rte. 50.

David Weinberg, senior planner for Cadillac Fairview, told the board his company plans to share the costs of such improvements with Costain Ltd., which hopes to develop the northeast corner of the intersection.

After repeated questions from the board, however, Weinberg said Cadillac Fairview would not foot the entire bill for the changes if it did not reach agreement with Costain.

Local residents say they are worried that the proposed development would aggravate present flooding problems along the Holmes Run Stream flood-plan, which bisects the proposed development site, and would add to runoff pollution of Lake Barcroft.

Cadillac Fairview has proposed building three drainage ponds on the land, to catch runoff and thus prevent additional flooding.

The company's plan calls for 2.25 million square feet of nonresidential space, with about 1.9 million square feet set aside for offices.

The Providence District Task Force has recommedded limiting nonresidential space to 2 million square feet and reducing the number of dwellings to 400. Another area of disagreement between local residents and the developer is the density of housing along the northeast edge of the site. The company has proposed 8 to 12 dwellings per acre, and the task force has recommended a limit of three to four units per acre.

If it approves the amendment to the master plan, the board will consider the Cadillac Fairview proposal more carefully before the rezoning application hearing, now scheduled for October.

Mike Kowalsky, a member of the task force and of the Holmes Run Civic Association, told the board Monday, "We don't want to gamble our communities on highly theoretical solutions. What disturbs me is the innuendo that Cadillac Fairview will walk away if they are not given what they want. If they do walk, so what?"

The supervisors are expected to vote on the proposed amendment at their meeting next Monday.