The body language was unmistakably clear. The audience sat with tightly crossed arms and legs, listening to the broadly gesticulating developer unfold his plan. The developer was offering the residents a deal they might refuse.

Last Thursday evening, nearly 100 Fairfax County residents gathered at a tense meeting to discuss with county planners and officials of the Cadillac Fairview Corporation on proposal to develop part of an area at Rte. 50 and the Beltway known as the Chiles Tract.

The land is now owned by the development firm of Wills and Pland, but officials of Cadillac Fairview say they have a contract to purchase the 190-acre site, located on the southeast quadrant of the tract. The purchase agreement is contingent upon county approval of Cadillac Fairview's development plan.

Cadillac Fairview, a Canadian-based company and one of the largest real estate developers in North America, wants to build a 2-million-square-foot office complex, a 500-room luxury hotel, a small retail center and approximately 250 townhouses on the site.

However, before any construction can begin, the county masterplan -- a broad outline of county building objectives -- must be amended and the tract rezoned. An amendment to the masterplan, county planners emphasized, does not ensure that Cadillac Fairview will be allowed to go ahead with its proposal. Instead, it provides the county with an option to build a major employment center, such as the one proposed by Cadillac Fairview.

The southeast quadrant of the Chiles Tract is bounded by Rte. 50 (Arlington Boulevard) on the north, the Beltway on the west, the Holmes Run Woods neighborhood on the south and the Broyhill nieghborhood on the east.

Currently, the county masterplan permits only low-density development -- three to four units per acre -- in the district. Under these restrictions, county planners said, 350 single-family homes could be built, a much smaller development than that proposed by Cadillac Fairview.

Controversy surrounding development of the Chiles Tract is not new. The land county planning commissioner William Lockwood said, is one of the most studied sites in the Washington metropolitan area. Despite the county's large-scale bid to attract business to Fairfax, four development plans for the tract have been rejected in the past 11 years, Lockwood said. Each time, the objections were the same: traffic congestion and flood problems in the area.

The wooded site currently is accessible only by the already over-burdened Rte. 50 and is bisected by the Holmes Run Stream Valley, which runs off into the surrounding residential areas on the southern edge of the Chiles Tract.

The artillery used to combat the developer's promises was no different last week. Speaker after speaker subjected developer and county planner alike to a barrage of questions about environment and traffic.

The proposed amendment to allow higher density development, county planner Ed Byrne said, recognizes that substantial road improvements would be a prerequisite to any plan approval. Byrne also said any road construction would have to be coordinated with plans for the undeveloped northeast quadrant of the tract.

Cadillac Fairview officials estimate that under their plan 6,000 additional persons would be working in the area each weekday. To compensate for that increase, Cadillac Fairview senior planner David Weinberg said the plan would include the following improvements:

Widening Rte. 50 to six lanes from Gallows Road to several hundred feet east of Jaguar Trail.

Building on overpass which would connect the northeast and southeast quadrants of the Chiles Tract.

Adding an extra east-bound lane under the cloverleaf interchange at the Beltway and Rte. 50.

Providing shuttle bus service between the sites and the Dunn Loring Metrorail station scheduled to open in mid-1985.

Cadillac Fairview and Virginia highway officials have begun preliminary discussions about the improvments. Whether the changes are approved by the highway department will play a crucial role in the chances of the current proposal. Last year, the department's rejection of another plan for the site sealed its death, said county planner John Duffy.

In addition to traffic improvements, Weinberg gingerly assured the growling neighborhood cavalry, the plan includes a flood-management program -- approved by the county planning department -- which would ensure that water run-off into the southern neighborhoods would be no greater after construction is completed than prior to it.

Weinberg said a constant flood water level can be maintained by installing drainage ponds around the site, using porous asphalt and preserving as many trees as possible. Restricting all non-residential building to the west side of the Holmes Run Stream Valley should also reduce drainage, Weinberg said.

Responding to audience members' fears that a concrete monster might be looming in their backyards, Weinberg explained the buildings would be constructed according to a "campus-like" design. The campus layout, Weinberg said, would include spacing the buildings far apart, preserving a minimum 200-foot buffer zone of trees to screen the complex from the surrounding neighborhoods and limiting building heights to eight to 15 stories -- with the lowest buildings bordering residential areas.

Some audience members, however, were skeptical of Weinberg's promises.

"We're like campers going into a tent," said one man. "Each time we enter the picture changes.

"What assurances do we have," he demanded of Weinberg, "that you will stick to your promises?"

Byrne said that before any development proposal can be formally considered by the county, the masterplan amendment to allow development must first be approved by the county planning commission, which will consider the proposal June 18. It then must go to the Board of Supervisors, which will review the planning commission's recommendation July 21.

If the amendment withstands these two obstacles, Cadillac Fairview will then present its plan at rezoning hearings scheduled for October.

At that point, Byrne said, if the county decides to approve the proposal it can insist that certain conditions are met.