Drive out Rte. 7 on the way to Leesburg and it's easy to tell that Loudoun County is not the same place it was four years ago.

Fast-food restaurants, gasoline stations, and high-tech businesses have sprung up along the sides of the heavily traveled highway. Large housing developments have been carved into the sloping hills farther off the road.

Prompted by the growth in population associated with these changes, the Loudoun County Board of Supervisors, with deeply mixed feelings, has decided that it is time for yet another change -- in the election districts for the board itself.

"This is already overdue. Clearly we aren't meeting the principle of one man, one vote . . . . We've got a moral obligation to [that] principle," said Supervisor Andrew R. Bird III, a Republican from the Sterling district on Loudoun's eastern side. Much of Loudoun's new population -- and some say the county has grown nearly 20 percent since the last redistricting in 1981 -- comes from the eastern side of the county as the Washington suburbs continue their sprawl.

Last month, the Loudoun board unanimously directed the county staff to begin the process of determining Loudoun's population and drawing redistricting proposals, which County Administrator Philip A. Bolen said he will finish in time for the next supervisor elections in 1987.

Suburban Republicans such as Bird have made inroads into Loudoun's traditionally Democratic politics, a trend that the county's GOP hopes will be accelerated by the greater representation eastern Loudoun is expected to gain from redistricting.

Republicans already hold three seats on the eight-person board, and can consistently count on support from Supervisor Steve W. Stockman, an independent from Broad Run.

But board Chairman Frank Raflo, a Democrat from Leesburg, expressed little concern about the partisan implications of redistricting. "In local politics, I don't think most people care about a candidate's party. I know they don't in my district."

More significant will be the perspective that any new supervisors bring to the board, what type of county they believe Loudoun should be. Many citizens believe redistricting will shift the county's political center of gravity away from supervisors with agendas rooted in Loudoun's agricultural tradition. Empowered by the change would be the county's newcomers: development interests and the residents of suburban housing tracts.

This prospect frightens even some Republicans.

Supervisor James F. Brownell, a Republican representing the Blue Ridge district in western Loudoun, said of redistricting: "I don't look forward to it. We simply didn't have any other choice."

Brownell's concern is how a board weighted toward eastern Loudoun will approach the question of land use, which has emerged as the paramount issue in Loudoun politics. As expanding development pushes up the value of land in Loudoun, many politicians are advocating measures to protect agriculture from being crowded out.

Already Loudoun gives preferential tax treatment to farmers, and a new pro-farming proposal called transferable development rights is now facing the board.

TDR is designed to target growth in sections of the county, such as the eastern half, which already have the roads and sewers to accommodate new development, while protecting open spaces in agricultural western Loudoun. Critics charge TDR would crowd eastern sections of the county, unfairly lowering the quality of life there.

The heaviest opposition to the TDR proposal, which now seems to have the support of a majority of the board, has come from Bird and Stockman, also from eastern Loudoun.

Brownell and others fear that any new supervisor eastern Loudoun is expected to gain in redistricting would be similarly unreceptive toward special measures to support agriculture.

"They just don't agree with some of the long-established traditions about land use in this county," Brownell charged. "You can't help but think that [the new supervisors are] going to be people against farming."

Brownell's fears are well-founded.

"The thing [farmers] have to fear is whether agriculture is still a viable business. It has to stand on its own two feet without subsidies from the county," Raymond Hamrick, president of the Eastern Loudoun Business Association, said recently. Hamrick's organization was one of the key groups pushing the board to redistrict.

Supervisor Ann B. Kavanagh (D-Dulles), whose district includes large portions of eastern Loudoun but who has supported TDR and other pro-farming legislation, expressed similar doubts about the viability of agriculture.

"I think it's more of a truism than many people are willing to admit" that agriculture faces a grave future, Kavanagh said.

But it is not only on agricultural issues that greater eastern representation will change the priorities of the board.

Residents of eastern Loudoun will demand services from the county tailored to the growing suburban flavor of the county, including such costly items as road improvements, libraries, recreational facilities and greater police and fire protection.

"Most of the improvements that [the county has] already had in these areas came largely as a result of the suburban east," Bird said. "You have different kinds of expectations here."

Bird said that people who have recently come to Loudoun from different parts of the country tell him "they find it hard to believe that so many [services] are not provided."

Both Republican and Democratic supervisors said that to be successful candidates from eastern Loudoun will have to meet these new demands.

"The people that come from suburban districts are obviously going to have suburban interests at heart," Kavanagh said.

Many longtime residents of Loudoun, however, fear that the demands that transient suburbanites place on the county will hinder the board's ability to stake out a long-term agenda compatible with the county's historical identity.

"They're more interested in their immediate needs, not necessarily in the best interests of the county. [Longtime Loudouners] should be in a better position to understand what is best for the county. We can look beyond the end of our nose."

One Loudoun farmer, who said his family has lived in the county for generations, gave an even harsher assessment of the newcomers: "Most of the people in eastern Loudoun don't even know what county they live in. They just come and go."

Perhaps no supervisor feels the tension between rural and suburban Loudoun more than Kavanagh. Her Dulles district includes the enormous Countryside housing development, but also stretches for miles to the west, encompassing many farms. Describing the task of representing such a diverse district, Kavanagh said, "It's like walking on a razor -- barefoot."

But Kavanagh said her experience teaches her that it is possible to reconcile Loudoun's competing interests. On the issue of road improvement, for example, there is a countywide need, Kavanagh said. "There is a community interest . . . . It's a matter of public education to make everyone understand what the benefits are."