Fearful that their land is acquiring a split-level personality, a group of Virginia farmes have taken the unusual step of going to court to stop a subdivision.

The suit is attracting attention because its outcome may define how far localities on the Virginia side of metropolitan Washington can go in keeping suburban development out of agricultural areas and channeling it into a already established urban sectors.

The decision could be critically important to still largely rural Fauquier County, which, with the extension of Interstate Rte. 66, will be less than an hour's commuting time from Washington. Already the county's cornfields and pastures are dotted with the hosues of suburbanities who want a taste of country living.

In southern Fauquier, 6 3/4 miles from the nearest school, 373 acres of fields and pastures are scheduled to be converted into the subdivision of Partridge Run Estates.

Patridges Run Estates is the immediate target of the suit filed by five farmers and the Mid-Fauquier Association, a citizen group, against the Board of Supervisors, who approved the subdivision.

But there is a larger objective. As the group's attorney, Allan H. Olson, says: "If the supervisors' decision is allowed to stand, basically there can be a subdivision anywhere in the county."

"This could be a very important case for the state of Virginia," says attorney Karen Edgecombe, one of the two land-use specialists assisting Olson. "It's an attempt by the citizens to make the Board of Supervisors more accountable when they are running scared."

One of the plantiffs is Rebecca George, a sprightly farming widow whose spread is only a mile from where Patridge Run Estates would be built. "What people fear most," she says, "is that one by one the farms are disappearing. That's the heart-breaking thing - that's why this is so important a test case."

The owners of all the properties surrounding the proposed subdivision have joined in the suit, including Michael W. Catts, whose 50-acre farm would be completely surrounded by the development.

Their argument is that the Fauquier master plan calls for the protection of the county's agricultural economy and recommends that development be confined to "service areas" surrounding the city of Warrenton and urbanized towns.

Because Patridge Run Estates is in an agricultural area and miles from any service area, their argument goes, the subdivision should not have been approved.

That's pretty much how the Board of Supervisors - the defendants in the suit - felt in November 1977 when they first voted against the subdivision. Then the developer, L.J. Clavelli, sued them. Told by their attorney that the developer had a good case and taht they could be held personally liable, the supervisors reversed themselves last April and approved the subdivision.

The supervisor's counsel said Partridge Run meets the "technical requirements" of the rules governing subdivisions and that the master plan is a "guideline," not a "legal requirement."

The subdivision would not violate any zoning limitations. In Fauquier, agricultural land automatically can be developed as densely as one dwelling unit per two acres, which means that every farm is a potential subdivision.

"I suppose that would be a contradiction if you thought agricultural land should be preserved," said county planning director Richard E. McNear, "but not if you looked at it from the point of view of how much you can control and deprive an owner of his right to his property."

As McNear says, land outside the developing areas has become more desirable to developers "because you not only have people looking for a home, you have those who are looking for a piece of the countryside."

There also is pressure on the countryside because the main urban corridor - along Rte. 28 - has inadequate public sewer and water facilities. When developers have to buy large parcels to make a septic sewage system work, it is cheaper for them to look for land in remote rural areas than in urban corridors.

For many residents of the county, including those suing the supervisors over Patridge Run, scattered development will cause a steep increase in the cost of services - and therefore taxes.

Samuel Butler, a dairy farmer and one of the five supervisors (he noted for Patridge Run, reluctanly), expresses the dilemma he and his colleagues faced:

"There's no way they [new residents] will pay their own way. Other people will have to pick up the tab. But what are you going to do? A man has the right to develope his land."

Supervisor Robert L. Gilliam, one of the staunchest supporters of new development in the county, says the revised comprehensive plan, which called for reduced growth pressures by shrinking and even eliminating service districts, actually encouraged leapfrogging to the rural areas.

"It is cheaper to buy 10 acres outside the service districts than one acre inside them," he said.

Gilliam also disputes the widely held assumption that Fauquier is an agricultural county. "Farming is not the basic income of the county," he says. "If you take the service industry it far exceeds income produced through agriculture. Today there are 10,000 to 12,000 people in paid jobs. There are less than 1,400 employed in agriculture."

The rising price of land, Gilliam says, is driving agriculture out. "If it takes 2 to 2 1/2 acres to graze an animal, how can you take land that costs $2,000 an acre and put it out to grazing?" he asks. "It's not economical."

The argument on the other side is that good agricultural land should not be sacraficed for more subdivisions at a time when food production is critical to the nation's eonomy.

One of the biggest boosters of agriculture in Fauquier is county agent Mike Keith, but even he sees limits. "About one-third of farmland is sitting on soils that could be put to better use," he says. "The large tracts of prime soils in the norther part of the county - they should be protected."