Bulldozers seem to be following the Hayes family. When they quit the suburban sprawl of Sterling Park two years ago for a home by a lake with views of the Blue Ridge Mountains in western Prince William County, they thought they had purchased some rural peace.

Now, that country life style is threatened.

Developers have filed various plans that would increase the population of the Gainesville-Haymarket-Catharpin area by 55 percent from 12,410 to more than 19,000. "And then to cap it all, there is a rock quarry proposed, right on our doorstep," said resident Valerie Hayes. "It's quite upsetting. I thought this was where I would want my two children to grow up. Now I don't know."

Hayes was one of more than 200 western Prince William County citizens who recently packed an elementary school cafeteria to discuss how growth is stretching its long fingers down the I-66 corridor to pull the Gainesville-Haymarket area closer to metropolitan Washington.

Hayes and many of her Lakeview Estates neighbors are joining forces with Gainesville-area conservationists who have fought encroachments into Prince William County's horse and farming frontier for decades. They have a long list of developers to fight.

Seven proposals confront western Prince William's residents, who now are scattered on farms and in low-density subdivisions. Included in the proposals is that of Vulcan Materials Co., which wants to quarry stone from part of its 1,200-acre tract southwest of the I-66 and Rte. 29 interchange at Gainesville; a 751-home equestrian development called Saddle Run, proposed by Annapolis developer Donald E. Hunter; and a Robert Trent Jones-designed complex calling for three golf courses, 800 homes, a hotel/conference center and office parks on 775 acres he owns west of Gainesville beside Lake Manassas.

If all these developments are approved, they could add 6,900 more people to the western part of the county, plus the traffic that the millions of square feet of commercial development would bring, said county planner Julie Phillips.

Not everyone is opposed to growth, however. Jere Collins has kept horses for 34 years on her farm just north of Haymarket and said she "relishes" the prospect of growth. It means she can sell her large home and move to a manageable town house in Haymarket to retire, she said.

Eileen Kovacs, a Lakeview resident, said she is looking forward to new neighbors and stores nearby, as long as the growth is well-managed. But development opponents are adamant that growth will destroy their pastoral retreats.

The Saddle Run proposal, scheduled for a hearing before county supervisors on Tuesday, has become the touchstone for their cause. Letters to local newspapers condemn the Hunter development as an attempt to turn the western part of the county into another Dale City.

"You may witness the raping and pillaging of our county by the Annapolis developer," wrote David A. Germond, a Catharpin resident. Speakers at public hearings have warned that the approval of Saddle Run would be the breach in the dike that now holds back a deluge of development.

Anne D. Snyder, a Catharpin resident and unofficial leader of the conservationists, said that if the county approves the Saddle Run project it would be a breach of faith with citizens and the federal government.

Snyder said the county made an agreement with the Environmental Protection Agency (EPA) in 1979 to limit growth in the Gainesville area to 2 percent a year in return for an EPA grant worth more than $3 million to fund extension of a public sewer line to Haymarket, where officials had said failing septic fields were a health hazard.

Because sewer lines frequently precede intense development, Snyder helped lead a drawn-out fight against the line. G. Richard Pfitzner, county board chairman, dismisses the resurrection of the battle over the sewer line extension as a desperate effort to halt inevitable growth in the western part of the county.

"They are opportunists who are opposed to anything. You can't deal with them," Pfitzner said. Michael Chern, an EPA spokesman, said the 2 percent growth figure was used only to size the line; it did not impose a cap on growth in Gainesville.

Furthermore, the county abandoned that growth limit this spring when it amended the county's comprehensive plan, the guideline for county development, said Roger Snyder, the county planning director, who is not related to Anne Snyder. That plan designates the I-66 corridor from Gainesville to Haymarket as an employment center, surrounded by suburban residential development.

In some ways, county officials see Saddle Run opponents as the last troops left from battles fought in the 1970s. In that decade, anti-growth activists could muster several hundred people to oppose projects such as Marriott Corp.'s King's Dominion-style theme park proposed for land alongside I-66 east of Gainesville, Roger Snyder said. Citizens challenged that plan in court before Marriott withdrew the proposal.

By contrast, only 15 to 20 people turned up at recent public hearings before the planning commission on the Saddle Run development. Pfitzner credits better county planning and the high-quality projects for the apparent decrease in the number of opponents.

"The fears of the '60s and '70s over theme parks are not the ball game today. It's high-tech parks and international golf courses," he said.

Nonetheless, this latest concern over growth in the area comes as no surprise to former county supervisor Alfred J. Ferlazzo, 73. Western Prince William County has always been a bastion of no-growth, said Ferlazzo, a board member for 18 years who retired in 1972. "They are pretty fixed in their ways up there, and this is the last say for these people to say, 'Leave it as it is,' " he said.