The Fairfax County Board of Supervisors voted yesterday to deny a developer's request to extend sewers into an area of the environmentally sensitive Occoquan watershed.

Although the County Planning Commission favored allowing the sewers in, county planners and attorneys argued against it, saying it could set a precedent for future sewer expansion and increased development in the 41,000-acre watershed.

In 1985, a Circuit Court judge ruled that Fairfax could severely restrict development in the rural southwestern quarter of the county, where runoff drains into the Occoquan Reservoir, to protect the drinking water for about 600,000 Northern Virginians.

In voting 7 to 1 to prohibit sewer service for the proposed 1,185-acre Balmoral subdivision, the board essentially killed the development as designed. Several civic and homeowner associations in the immediate area favored the sewer extension, which they said would better protect the land and water than if the developer, N.V. Land Inc., had to use septic fields.

County staff members, although commending the project overall, said in a report that the county's comprehensive land use plan prohibits expansion of sewers into the area of the proposed development.

The developers wanted to build 195 houses priced from $750,000 in clusters around a 200-acre private golf course, a recreation center, pool and eight tennis courts. Grouping the houses in clusters would allow preservation of large areas of the property in the natural state.

Francis A. McDermott, attorney for the developer, said after the vote, which he called "a mistake," that without sewers, houses would have to be spaced further apart to accommodate septic fields, which would be more detrimental to the immediate environment and the water supply.

McDermott said his client now would have to have a conventional development with septic systems or go to court to try to have the board's decision overturned.

Supervisor Elaine McConnell (R), whose Springfield District contains the site of the proposed development, was the only board member to vote for the expansion, saying a majority of residents in the area favored it. Lilla Richards (D-Dranesville) did not take part in the debate because of a possible conflict of interest that the county attorney did not have time to rule on.

In an unrelated case yesterday, the board approved rezoning and a conceptual development plan for a 114-acre commercial and residential development adjacent to the future county government center near Rte. 50 and I-66. Although final plans for the development have not been approved, the conceptual plan calls for a 1.7 million-square-foot development, one third of which would be residential, in an unspecified number of low-, mid- and high-rise buildings. The focus of the development would be a "landmark tower" that might be as high as 17 stories, or 230 feet.

A key component of the project is a transportation management system that would coordinate development with transportation improvements in and around the development. The developer, Sequia Building Corp., and the board have agreed that occupancy permits for finished buildings could be withheld if adequate transportation improvements have not been completed.