Pierre Billard, owner of a 19th century farmhouse in Fairfax County, thinks his home may have been used as a headquarters for the Union Army during the Civil War. But instead of fighting to get listed in the Fairfax County Master Inventory of Historic Sites, Billard is trying to decide what to salvage when the bulldozers come rolling down Ridge Top Road.

Tucked in behind Rte. 50, Billard's land sits at the heart of what county planners hope will become the political, cultural and commercial center of Fairfax County within 30 years. With a land-use plan now in place that would permit developers to increase building densities in the 5,000-acre area around the intersection of Rte. 50 and I-66, Billard is beginning to get inquiries about his 7.1 acres of prime commercial land.

"My mother had an inkling this place would be a good investment," said Billard, whose property has more than quintupled in value in six years. "But my parents bought the farm as a place to live. I'm going to stick it out as long as I can, but I don't think it will be more than 10 years before life becomes unbearable here."

For the 20-odd homeowners here caught in the riptide of development, there are two alternatives: either choose to live with the changes, or sell the half-acre homestead and head for the hills, or at least to Fauquier County.

But Billard and his neighbors are finding that selling -- getting involved in the roulette wheel of land speculation -- can be a tough game. The uncertainties of timing and opportunity have made life difficult for the residents whose land is becoming too valuable just to live on.

In an effort to head off problems between residents and developers, the Fairfax County Board of Supervisors appointed a task force of citizens, developers and county staff to develop a plan for an "urban village" in the largely undeveloped Rte. 50/I-66 area.

Although the plan, adopted last summer by the County Board, protects existing residential subdivisions, some homeowners in the area say they would rather sell than live in the shadow of high-density development.

"We love the house," said Billard's friend Gloria Mills. "But who wants to live across the street from a 200-room hotel?"

For the families who have lived for 25 years in the park-like enclave -- complete with deer, native trout and red-tailed hawk--the signs of change are impossible to ignore.

Already, Ramada Inn has obtained county approval to build a hotel at the end of Ridge Top Road, and land along the road is turning commercial as landowners begin to cash in. When A&P Water and Sewer Supplies Inc. bought a 10-acre site across from Billard in 1980 the land jumped from an assessed value of $188,070 in 1979 to $449,595, the result of rezoning the land for commercial use.

"The noise and pollution from Rte. 50 is so bad we don't use our back porch anymore and I have to keep the house closed up," said Wacuba Looney, a resident of the small, 17-home Random Hills subdivision adjacent to Billard's road. "And that's just the beginning. We hate to see it happening. If we're going to be pressured out, we'll sell."

For the three families who own homes and live along Ridge Top Road, now planned either commercial or industrial under the 50/66 plan, there is little question of staying. The road abuts the 183-acre county site for the proposed governmental center, the future administration headquarters for Fairfax County. Although plans for the center were put on hold recently by county supervisors concerned about overspending, the land-use plan adopted by the board keeps the governmental center as its keystone.

"There will probably be low-rise office space along here," Billard said, waving in both directions down Ridge Top Road, now just a gravel track.

When the county bought the site for the center in l980, Billard's land almost doubled in value, despite uncertainty over the county's plans. This year, Billard's land is assessed at $16,116 an acre. Just across Ridge Top Road from his property, the l0-acre tract owned by A&P Water and Sewer is assessed at $47,916 an acre.

The three families on the road may not share equally in the bonanza.

The Richard Robertson family is one. Robertson owns three acres, a house and a few spare tractors across the road from Billard. But one proposed alignment for the Springfield Bypass, the proposed four-lane highway that would link Reston with Springfield, would lead the road right through Robertson's front porch. Robertson's land, in those circumstances, would end up being sold at residential prices.

His next-door neighbor, Franklin Ramey, on the other hand, would have seven acres of land--adjacent to the highway -- that he could rezone commercial under the Rte. 50/I-66 plan.

"My property quadruples in value if the bypass goes in here," Billard said. "I'm going to get it in the pocket, but Robertson will only get what the county pays him."

For the homeowners of Random Hills, a neat, wooded subdivision where most of the homes are owned by people who bought them new 25 years ago, the question is whether to try to keep the community intact as a subdivision. The Rte. 50/I-66 plan would allow them to stay, but if the plan develops as proposed, they would eventually border one of the densest parts of the county.

"Most of the people in this community expect to sell commercially," said Looney. "That's the only way the land will really increase in value: if it goes commercial."

But many Random Hills residents are confused about how and when to sell their acre lots. They say that pressure from developers, who they believe are eager to buy up lots, and disagreements between neighbors may make it impossible for them to control the outcome.

Verlin Smith, a realtor who was active on the Rte. 50/I-66 task force, said that a home in the Random Hills subdivision would probably sell for two to three times its residential value if residents agree to rezone commercial.

"Some residents want to hold out, to sell later when the land will be more valuable," said one homeowner who did not want to be identified. "But some people may not be able to wait, and we know it would be better to sell as a block rather than separately."

Another problem is the prospect of the neighborhood becoming depressed as investors buy up homes and rent them while waiting to resell as commercial land.

"Pretty soon it's going to be so valuable we're not going to be able to afford to live on it," said Kay Hogan, who has lived in the subdivision since 1955.

"This is a problem for people rooted in a community, but their days are numbered," said Smith. "Their best interest would be served by a concerted effort to get together rather than have individual investors buy up the houses as they come available -- which they will over the years."

"It's real country out here, and the people like their privacy," said Billard, looking across the fields and woods of the place where he grew up. "But I'm already looking for a place farther out . . . . Whoever buys this place isn't going to be interested in the house or the trees or anything else on it. They'll be buying the land."