When Ron and Libby Sanders were searching for a suburban home last autumn, they looked no further than a Prince William County site of flowing mountain laurel trees, teeming with wildlife, near the Occoquan River.

"The trees are what brought us," said Libby Sanders yesterday. "You could get up in the morning and hear birds singing and squirrels chattering. It was really a lovely place."

Now, she says, the sounds of forest life off Antietam Road in the planned community of Lake Ridge are drowned out by bulldozers -- knocking down the trees she loves. She was one of 50 neighbors who picketed the 35-acre construction site last week in a futile effort to save the trees.

It is yet another case of young families seeking to leave the congestion of Washington for the pastoral existence of a quite outer suburb, only to discover that development in rapidly growing Prince William County is only a step behind them.

The disputed site straddles Antietam Road. Ridge Development Corp. and Pulte Homes Corp. of Tysons Corner plan to build 192 condominiums on the eastern plot, and 120-single-family town houses on the west side, said Tony Sala of Ridge Development.

The Sanders and others who moved into Lake Ridge in recent years say they were never told that new construction might someday mar the leafy setting outside their windows.

"It seemed like a great place to raise kids," says Karen Buczek, who adds that her family moved there two years ago "with the understanding that a lot of the community's grounds would be left with trees."

Libby Sanders said that the neighbors asked Pulte to consider lowering the density of the units in order to make room for more trees, but "they couldn't believe that we would ask them such a thing."

"I don't think anything was accomplished with them," Sanders added. "Now I look out my window and see trees. Fairly soon it will probably be a parking lot."

Sala said yesterday that Lake Ridge Development in 1969 had planned a 3,000 acre, 10,000 unit community to be built by assorted contractors.

At that time, according to Prince William County zoning officials, the area west of the town of Occoquan was virtually undeveloped. Sala said approval of high-density zoning permitting 10 town house units per acre, was gained at hearings in 1969 and 1970.

Concerned about the possibility of overdevelopment, the Prince William County Board of Supervisors amended the density level to only six town house units per acre in 1972, but the decision was not retroactive, said Lorene Payne, a zoning inspector.

Unlike neighboring Fairfax County, Prince William has no tree preservation ordinance. A draft ordinance based on the Fairfax law, which provides for regular on-site inspections and penalties of up to $1,000 a day for violations, was rejected by county supervisors in 1976 as too costly to enforce.

Sala acknowledged that Ridge Development has been stung by the wrath of the residents. He emphasized that one-third of the total 3,000 acres will be left "virtually undisturbed," and that Ridge is simply carrying out the plan developed more than a decade ago.

"We had planned to have built all the units in 10 or 12 years, but only 4,000 have been built," said Sala, blaming the housing industry's economic downturn for the community's slowed growth.

"Our density factor is well below the allowable limit," sala said. "We will build 1,000 to 1,200 less than the total we planned. There will only be seven town houses on each acre. What we planned were units affordable for first-home buyers in the $60,000 range. It would be economically unfeasible to save more trees. If we build less we will have to raise the price of the homes."

But those arguments don't wash with residents who complain that the rabbits, opossums and occasional deer that roam among the wild azaleas, dogwood and pine trees near their homes will soon be gone.

"I don't like it," said Karen Omir, a Lake Ridge resident for the past two years. "The builder has a legal right to do this, but people have a right to show their displeasure."

Ron Sanders agreed, adding, "It takes a lot to get a bunch of middle-class people on a picket line."