The Prince William County Board of Supervisors last week unanimously approved a $72,000 appropriation to build a four-foot-wide bicycle and foot trail along Old Smoketown Road and Cavalier Drive in the Lynwood development, a move that two supervisors called "a dangerous precedent."

The two supervisors are concerned, they said, that other communities will make the same request, although Lynwood residents "deserved an exception" because of circumstances "beyond their control."

In August more than 800 Lynwood residents formed a protest movement against the county's comprehensive plan that called for an extension of Smoketown Road, saying that such an extension would pose a safety hazard for the children of the community. At that time, protest leaders called for making Smoketown Road a cul-de-sac at Cavalier Drive to prevent traffic from going through their neighborhood. The road, originally designed to carry 3,000 cars a day, could carry as many as 13,000 vehicles once Smoketown is connected to Davis Ford and Old Bridge roads.

A factor in the county's insistence on the extension is the slated opening in July of Potomac Mills, expected to be one of the largest manufacturers' outlets in the country. The extended road will be the most direct route to the mall, traffic planners say. Last summer the board approved a rezoning request by Old Bridge Estates, whose developers requested that plans for the extension go forward. The developer plans 616 housing units on a 173-acre tract in the area.

According to county planner Roger Snyder, the plan to extend Smoketown Road was approved by the Lake Ridge-Occoquan Civic Association in 1979, before most of the land had been developed. Since then, the county's design and construction standards manual has been updated to prohibit homes from fronting on an arterial road such as Smoketown. The Lynwood community would not have the traffic safety problem it now faces if the new manual had been in effect when the development was built, officials said.

The bicycle and foot trail is a concession to the cul-de-sac request, the board said, but should not be seen as a precedent. Said Woodbridge Supervisor Don Kidwell, "I guess we owe it to them Lynwood residents because the county has some culpability in this and they sort of got caught in a crack. But I'm worried that other areas will want the same thing." Dumfries Supervisor Ed King voted for approval, while calling the move a "dangerous" one. "Other areas need sidewalks more critically on the face of it. I have deep, deep reservations about this."

It is uncertain who will maintain the new path, according to traffic planner John Schofield. The planning department will meet soon with the Lake Ridge Park and Recreation Association to decide that, he said. "They already have some bike paths that the new one might connect with and they maintain those," he told the board. Occoquan Supervisor Kathleen Seefeldt, who made the request, said the Ridge Development Corp., which built the community, will donate $10,000 toward a detailed engineering study of the trail site.

The board also approved a $1.5 million budget appropriations for the school administration complex to be built at Independent Hill.

In other business, the board authorized a $9,211 grant application for family subsidized housing for mentally retarded adults. In his request, Robert Dirks, community mental health executive director, told the board that there are 400 mentally retarded adults in the county, 100 of whom are in immediate need of residential services.

The program allows independent life styles for such adults and is paid for partly by the county and partly by the families involved. Currently, 25 mentally retarded adults are served in the program, which is in its second year.