Picture this: out-of-town speculators buying up large tracts of northeastern Loudoun County, where some secondary roads are made of dirt and it seems like it takes forever to get to Fairfax.

That was the Catoctin region in the 18th century, and to a degree that is the Catoctin region today. Most residents agree that the ageless charm of their picturesque agricultural area is what makes them so proud to live there.

But controversy has split this peaceful community dotted with old buildings, natural springs and large limestone rock outcroppings. The dispute, over the establishment of a historic district, has caused hard feelings that may take some time to heal.

State officials earlier this month approved the 25,000-acre Catoctin Rural Historic District, recognizing the historic significance of the area bounded roughly by the Potomac River on the north and east, Leesburg on the south, and the top of the Catoctin Ridge on the west. The area is divided by Rte. 15.

Members of the relatively new group Friends of Route 15, which prepared the application for the historic district designation, had thought it would encounter no resistance, locally or in Richmond. Not so.

Many of the nearly 500 families living in the area have come out in opposition to the state's action and a proposed federal designation, saying they fear that the moves will open the door to restrictions on their properties.

Friends of Route 15 and county and state officials say that won't happen, but the opponents say they are determined to stop the listing of the district on the National Register of Historic Places.

The opponents include families who for generations have farmed the region from small homes as well as on large estates. They are normally a quiet group, so their vocal opposition to the rural historic district, an honor emphasizing the importance of agriculture in the region, has particularly surprised proponents.

At the heart of the opponents' concerns is the specter of approval by the Loudoun County Board of Supervisors of a third designation for the area -- a County Historic Overlay District. That designation, which the state's action makes possible, could lead to architectural review requirements or additional land use regulations for property owners.

In a statement issued Dec. 12, the day before the state approved the historic designation, five county board members said that "there has been no request for the board to consider" a county overlay district. Catoctin District Supervisor Betsey Brown (D) says she would oppose such a request.

But opponents haven't been swayed. "There definitely are overlays coming" in Loudoun, said area resident John J. Whitmore. In a recent letter to other residents, he wrote that "restrictions may include getting permission to paint or change the color of buildings, fencing requirements or permission to erect or demolish a building."

Whitmore and another local resident, James C. Athey, said they never received an April 1987 letter that Friends of Route 15 says it mailed to all area residents describing the purpose of the proposed state and national historic designations, and they say residents will continue to write letters in opposition to the national district.

"We have very good hopes we can stop it from getting on the National Register," Athey said.

For that to happen, more than half of the property owners in the affected area would have to send individual letters to the state Division of Historic Landmarks. Petition signatures don't count, said Margaret T. Peters, a spokesman for the agency.

Peters, who said there may be close to 1,000 property owners in the area, said the division had received about 150 letters as of last week. She said letters will be accepted until early January.

"The application clearly met the criteria for the National Register," she said, and ordinarily would be submitted automatically after its acceptance by the state.

Blocking national designation would not prevent local officials from establishing additional land use restrictions.

Activists in Friends of Route 15, who prepared a detailed application to the state, say in retrospect that they wish they had sent a second mailing to local residents before the Dec. 13 vote by the Historic Landmarks Board in Richmond.

There was an informational meeting in the Lucketts Community Center shortly before the Richmond action, but some people feel that "public notice probably wasn't given as it should have been," as Whitmore put it. That led to an atmosphere of mistrust, some residents said.

And there's the western bypass issue. Opponents of a national historic designation say Friends of Route 15 is motivated by a desire to stop the proposed bypass, one alignment of which would slice through the district. However, the Route 15 group says that the designation would only add a little red tape for federal highway officials, but would not stop construction of a bypass.

Judy Gerow, who spearheaded the volunteer effort to document the Catoctin area's historical treasures, noted that the area is the second largest rural historic district in the state, behind the Madison-Barbour district in central Virginia.

She cited round ice houses, eight-sided meat houses and other structures created from native materials, plus the Catoctin Iron Furnace.