A parade of Loudoun County residents, mirroring the diversity of the rapidly growing county, vented their opinions last night on a controversial proposal designed to blunt the encroachment of development on the county's open spaces.

Transferable development rights (TDR), alternately praised and blasted at a public hearing before the Loudoun Board of Supervisors in Leesburg, are designed to channel growth to sections of Loudoun where development is already under way, while placing permanent restrictions on growth in rural sections.

Although its boosters hope the plan will forge a compromise between agricultural and development interests, last night's hearing seemed to capture the tensions that have arisen since Loudoun began its development boom. Real estate brokers and residents of suburban housing tracts in eastern Loudoun protested the proposal; farmers and spokesmen for conservation groups spoke passionately about the need to save open space.

"I don't think that eastern Loudoun should be a Baileys Crossroads or a Tysons Corner," said David McWatters, a real estate official. " . . . We don't want it."

Edward Polen, president of the Loudoun Farm Bureau, countered that TDR "is the answer to the preservation of open space and farming in this county."

The board deferred action until early January. Both supporters and opponents on the board said in interviews that they expect a TDR proposal will pass the board, most likely by the same 5-to-3 split that has marked other recent votes over the county's agricultural policy.

Because local Virginia jurisdictions do not have home-rule authority, the board must submit a proposal to the General Assembly by Jan. 8 to seek enabling legislation that would allow it to enact a TDR law.

TDR would work by allowing landowners with more than 50 acres to sell the right to develop on their property. The purchaser, a developer, then would use the development rights elsewhere to build at a higher level of density than would be allowed under normal zoning rules. After a landowner had sold his rights, a permanent restriction on development would be placed on his property.

As proposed, this restriction could be reversed only after a minimum of eight years and after the landowner purchased development rights from some other property.

TDR programs have been implemented in only a small number of jurisdictions around the country. One of these is Montgomery County, where a TDR experiment at Avenel Farms was a source of controversy for years before a judge approved the transfer last July.

The unorthodox nature of TDR insures that it will face rough sledding once it goes to Richmond. State Sen. Charles L. Waddell, a Democrat who represents Loudoun and has said he will sponsor TDR, said in an interview yesterday: "The prospects are uncertain . . . . The assembly has been very reluctant to experiment with land use proposals."

Although legislation in Richmond would be tailored specifically to Loudoun, Waddell said many legislators fear the precedent it would set. "Many who oppose this see it as a 'nose under the tent' scenario . . . . They say 'you kill a snake when you find it.'"

Loudoun Board Chairman Frank Raflo repeated his stance yesterday that a TDR program would mark the ideal marriage between developers and open spaces. "The chances in Richmond are good. There is a growing recognition that the preservation of land is an important element in the economic well-being of the state."