The Fairfax County Planning Commission has voted to permit construction of sewer and water lines in an area of the Occoquan watershed, a move that county staff members said could set a precedent for future expansion in the environmentally sensitive area.

County officials said Thursday night's decision, unless overturned by the Board of Supervisors, would mark the first time that new public water and sewer lines would be permitted in the 41,000-acre watershed since a 1985 court decision known as the Occoquan downzoning. In that case, a circuit 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 of some 600,000 Northern Virginians.

Critics of the Planning Commission's action expressed concern yesterday that it will open the door to additional sewer construction and pressure for higher density development in one of the last open areas in the county.

"I think it's a kick in the guts to the whole Occoquan conservation process," said Denton U. Kent, deputy county executive for planning and development. "The reaction I've gotten so far from supervisor staffs has been one of surprise and incredulousness."

The Occoquan downzoning reduced development in the watershed from one house per acre to one house per five acres. Kent said the lower density was set "in order not to require public facilities that could pave the way for further development or {could provide} justifications for raising the density level.

"The concern is this could become a precedent folks use to leverage other justifications for sewers" in the watershed, he said.

The Planning Commission's 7-to-4 vote involves a proposed 1,185-acre development northwest of Clifton. The property is south of Compton Road on both sides of Union Mill Road.

Francis A. McDermott, the attorney for the developer, N.V. Land Inc., said yesterday that "the naysayers are losing sight of the ball . . . . The main purpose of the Occoquan downzoning was to protect the water supply, with the two primary methods being density limitations and preservation of the environmental quality corridor. Both objectives can be satisfied on this property only by approval of the request for sewering."

The proposed development, called Balmoral, includes 195 single-family houses priced from $750,000; a 200-acre private golf course designed by Ed Ault, who designed the Tournament Players Club at Avenel in Potomac; a recreation center, pool and eight tennis courts.

The houses would be clustered around the golf course. Though some lots would be smaller than an acre, the overall density of the development would be below one house per five acres because large areas would remain undeveloped.

Thursday night's vote was on allowing public water and sewer lines on the land. The Planning Commission is scheduled to vote on the development itself Feb. 3.

The county staff, in a report on the proposed development, said it "exhibits a commendable level of environmental protection through its sensitive design."

However, the report said that the county's comprehensive plan prohibits extension of water and sewer lines into the area, and the staff recommended that the developer use wells and septic fields instead.

Planning Commissioner Suzanne F. Harsel of Annandale, who voted against the application, said: "The plan says, do not provide public sewer and water service to the {area}. I see no reason to posture about other things. I don't see how it could be any plainer or clearer."

McDermott, the attorney for the developer, said the comprehensive plan does not specifically prohibit new water and sewer lines to the area. In a letter to the commission, he wrote that without sewers, the developer would have to spread the houses out to accommodate the septic fields. The process would require much clearing of land, he said, which would be more harmful to the environment.

Planning Commissioner Peter F. Murphy Jr. of the Springfield District, where the development would be located, voted for the application. He noted that the comprehensive plan is a land-use "guide" and said that there are "shades of gray as to how the objectives of the Occoquan {area} are to be met."

"Sewers, if done correctly, are much better to protect the ecology than randomly placed septic tanks," he said. "I'd be quite happy if the entire watershed were developed this way, with cluster development around golf courses."

Under Virginia law, planning commissions have the final say on matters concerning the "location, character and extent" of a county's comprehensive plan. However, Fairfax County officials said yesterday that the Board of Supervisors likely will hold a special hearing to review the commission's decision.