A group of almost 300 residents of Lake Ridge in the Occoquan District crowded the evening session of last week's meeting of the Prince William Board of Supervisors to protest the proposed extension of Smoketown Road.

Extension of the road is part of the county's comprehensive plan on land use. The planning office and the supervisors have been holding public hearings on the plan since last fall.

The extension, which would connect Davis Ford and Old Bridge roads, would carry as many as 13,000 vehicles a day through several developments in the Lake Ridge-Occoquan area. The road was originally designed to carry 3,000 vehicles.

Residents have been registering formal and informal protests with the planning office and the supervisors for months, saying the extension would intrude on their quiet neighborhoods and could even endanger the lives of their children. "One community activist told the board last week that if it didn't delete the extension from the comprehensive plan, it would be responsible for the deaths of babies," said county attorney John Foote.

According to county officials, the extension has been on the books since before the comprehensive plan was drawn up in 1982, but protests did not occur until the board last summer approved a rezoning request to allow the development of Old Bridge Estates, a planned community that would put 616 housing units on the 173-acre tract. The developer has asked that plans for the road's extension go forward.

Besides being a "collector street" serving the three subdivisions with access to it, the extended road would also be the most direct route to the Washington Outlet Mall. The mall, newly renamed Potomac Mills, is slated to open this spring off I-95 at the Dale City interchange and is expected to be the largest manufacturers' outlet in the country, county planners say.

Foote said that despite protests by 20 speakers, several of whom were quite emotional, the supervisors gave no indication they intend to scrap plans for the Smoketown extension.

The board approved a rezoning amendment to allow a 1,260 square foot sign for Potomac Mills to be moved 300 feet closer to the interstate. Developers told the board that the height of the sign will be lowered from 150 feet to 140 feet. The purpose of moving the huge sign is to attract travelers off I-95 more easily. The mall is expected to generate $10 million in state revenue and more than $4 million in county revenue, according to an economic analysis by the county's finance department.

In other business, the board:

* Approved public hearings for an ordinance that will make it illegal for an owner to allow a cat or a dog to defecate on private or public property without permission unless the owner cleans up after the pet.

* Honored zoning administrator Sager Williams, who will leave for a similar job in Austin, Tex., early next month.

* Commended a captain of the Prince William Fire and Rescue Service and two cardiac technicians for successfully resuscitating a 19-month-old baby during a house fire in Dale City Nov. 30. They are: Capt. Scott Davis, Robert Holman and Joseph Robertson.

* Approved a rezoning for Bank's Auto Parts, one of the largest auto junkyards in the country, according to officials, for expansion of the business from approximately 40 acres to nearly 60 acres. The owner will erect a 10-foot barrier fence and plant a buffer zone of trees along Smoketown Road.