Following months of debate that raised the specter of an east-west split in Loudoun County, the Board of Supervisors last week approved 5 to 3 a developer's proposal to increase the number of homes at an eastern Loudoun planned community in exchange for the preservation of 350 acres of western Loudoun farmland.

The proposal will be the first practical application of a controversial policy aimed at preserving farmland in a county increasingly concerned about losing open space to development.

The policy, called "density transfer," creates a landowner's right to subdivide, can be sold without selling the land itself.

Designed to direct growth toward urban areas and away from rural land, the plan would allow a developer to purchase subdivision rights from a rural landowner, and use them to increase the number of lots on his urban property.

The farmer would acquire new capital resources to help resist the financial pressures to sell out, and the county would get a conservation easement on the farmer's land, making the land unavailable for development thereafter.

The number of lots the developer could add to his project would not necessarily be the same as the number of development rights he had purchased.

That number would be determined by the normal rezoning process, with the supervisor in each case weighing the value of preserving some farmland against the increased costs to the county of providing services to more residents in the urban area.

Farmland preservation thus would be another inducement, along with others such as school and fire station sites, that developers could offer the county to obtain higher density.

Last week's board action approved developer James M. DeFrancia's proposal to acquire subdivision rights on 350 acres near Hillsboro owned by farmer Donald T. Virts. In exchange for the county's conservation easement on the land, DeFrancia, regional manager for 437 Land Co., would build an additional 112 town houses, adding about 4 percent to the previously planned 2,540 houses at Countryside, the largest development under construction in Loudoun County.

Voting to approve the proposal were board Chairman James F. Brownell of the Blue Ridge district, Guilford Supervisor Betty Tatum, Mercer Supervisor Thomas S. Dodson and Dulles Supervisor Ann Kavanagh.

Voting against the proposal were Sterling Supervisor Andrew R. Bird III, Catoctin Supervisor Frank Lambert and Broad Run Supervisor Steven Stockman.

Countryside lies in the Broad Run and Dulles districts.

During recent meetings, residents of Countryside and the surrounding area, most of whom accepted the density transfer concept, opposed DeFrancia's proposal for a variety of reasons.

Most said they did not want the additional 112 town houses in their community and that the county should not alter its 1978 agreement with 437 Land Co. regarding building density.

One Countryside resident called the proposal a "win situation" for western Loudoun residents and a "no win" situation for the east.

Before the board's vote, Bird said, "I'll be perfectly honest. Who benefits? Ask yourselves who benefits. Now does the whole county benefit because of 350 acres of farmland? . . . If so, then it's a pretty abstract benefit."

Agreeing with Stockman, Bird said there were "other options" that DeFrancia could have offered the county instead of the farmland preservation, such as public facilities. The other options, Bird said, would have benefited not only Countryside but "the rest of the county as well."

In a prepared statement before the vote, Kavanagh said she was "dismayed to see the specter of east versus west raise its ugly head again" over the density transfer proposal. She said the proposal would ultimately benefit the entire county.

Tatum recalled antagonism that surfaced in the early 1960s when Sterling Park, the county's first major development, was built over the opposition of many longtime county residents who resented the influx of new people and the development of what had once been farmland.