At the Washington area's western edge, officials were looking to boost a sagging economy in the early 1990s. They approved construction of a four-lane road running west from Dulles International Airport through thousands of acres of farmland and rolling hills, where businesses could build vast office parks.

Nearly four years after the Dulles Greenway opened, Loudoun County is slowly getting the businesses it wanted. But now the Greenway is luring something county leaders abhor: widespread housing development west of the road, in an area set against the Blue Ridge Mountains that Loudoun is desperately trying to preserve as rural.

"The Greenway has made it easier for western Loudoun to grow by leaps and bounds," said Supervisor James G. Burton (I-Mercer). "It's a double-edged sword. On the one hand, it attracts business, but on the other hand, it brings more people. . . . It hastens the pace of things."

As governments around Washington discuss plans to widen highways or create new ones, the results of the Dulles Greenway's construction illustrate two sides of their debate.

Slow-growth advocates say that big new highways like the Greenway have consequences well beyond where the asphalt ends and that such roads encourage sprawl by providing easy access to rural areas.

Supporters of new roads say they not only relieve traffic congestion but also focus development along a corridor, as the Greenway is starting to do. They also argue that development comes to many rural areas even without new roads, noting that rural western Loudoun started to develop before the Dulles Greenway opened.

Other communities will have to make their own assessments about the effects of highway proposals, such as Maryland's intercounty connector between Interstates 270 and 95 and Virginia's western transportation corridor between Stafford County and Dulles airport, which critics say would open rural areas to development.

In Loudoun, now the region's fastest-growing suburb, the economy was moribund when county supervisors approved the 14 1/2-mile Greenway in 1993. Supervisors thought the road would encourage dense business and residential development and the construction of a rail line, pumping up depressed land values.

The Greenway, which links the Dulles Toll Road with Leesburg, was built by a group of private investors. The road project was plagued by financial problems because commuters were reluctant to pay $1.50 for a weekday trip. But the number of drivers has been growing as development increases.

Since it opened in September 1995, the highway has helped lure businesses. Near the road, backhoes and bulldozers are pushing aside dirt to construct a 150-acre office, retail and housing complex for Reliance Development Group. Toward the eastern end, MCI WorldCom Inc. is building a massive office campus, and America Online Inc. is expanding.

Michael R. Crane, chief executive officer of the Dulles Greenway, said that because the road was built in advance of development, it has limited sprawl by channeling growth near Leesburg and between Route 7 and the Greenway.

But as the thriving economy helped stimulate housing construction, some county leaders became concerned that the channeling effect was working a bit too well and that Loudoun's ability to provide residential services around the Greenway corridor itself might be overwhelmed.

Last year, county supervisors cut by about 50,000 the number of houses that could be built in the corridor.

But the commercial development along the Greenway, and the employment that development is creating, also contributes to the residential construction boom underway west of the road. A representative of Garrett Development, of Stafford, said recently that he plans to build houses on rolling hills west of Leesburg that would be geared for sale to technology workers, particularly those at AOL and MCI WorldCom.

West of Leesburg, officials said, the road already has speeded home construction in an area that county plans say is supposed to remain rural. The number of residential building permits issued for the west has more than doubled from 214 in 1995 to 488 last year.

Many of these home buyers have figured out that if they take the Greenway, they can quickly commute to jobs in Reston, Tysons Corner or Washington--a trip of less than 40 miles that can be made made without hitting traffic lights if they take the Greenway, Dulles Toll Road and I-66.

County supervisors are concerned that this western development will gobble up Loudoun's most idyllic landscape and force rapid construction of many new schools and other facilities at significant taxpayer expense.

Shane Blackwell said he moved to Round Hill with his wife, Lisa, and two children for the less expensive housing, rural lifestyle and quick commute to a job, which at the time was in Tysons Corner. Blackwell's subdivision, the Villages of Round Hill, includes new town houses and single-family houses in a rural area near centuries-old stone houses.

"We wouldn't have made the move if the Greenway wasn't there," said Shane Blackwell, 39, who moved in November from Clinton. "Let's face it, the only thing that was accessible to us if the Greenway wasn't there is Route 7."

And he wasn't about to sit through the 30-plus stoplights between his house and the Tysons office.

Even as far away as West Virginia, developers said, the Greenway is a boon. Mike Bartlett, sales manager for Dan Ryan Builders in Jefferson County, W.Va., said most of the people buying his new houses are using the road.

"Ninety to 95 percent of those [buyers] are coming out of the Northern Virginia-Loudoun corridor and are willing to make the commute because of the Greenway," Bartlett said. "Combined with the difference in real estate taxes . . . these people are able to buy $40- or $50,000 more of a home for the same payment. It's worth that extra 20 minutes."

Controlled-growth activists say roads like the Greenway encourage the scattering of new houses in areas that do not have enough schools for the new residents.

"This spreading out is leading to an increased amount of driving with an increased amount of air pollution," said Stewart Schwartz, spokesman for the Coalition for Smarter Growth.

George L. Barton IV, who chaired the Loudoun Board of Supervisors at the time the Dulles Greenway was approved, said the Greenway's impact on western Loudoun did not come up when supervisors considered the proposal. "Western Loudoun was going to develop whether or not the toll road was there," he said.

Robert T. Grow, director of transportation for the Greater Washington Board of Trade, said roads need to be built to keep the economy moving. Grow said concern about development past where roads end should be addressed by local officials in their land-use plans.

"If you have a strong economy . . . if you have a growing number of people, and job growth is going to occur, what you need is the infrastructure to provide for that growth," Grow said. "You can't ignore it."

County officials said they are doing everything they can to deal with the development west of the Greenway. In fact, they've made it their top priority.

But some say they're constrained by existing zoning that allows for one house to be built on every three acres. County officials have endorsed proposals to boost western Loudoun's rural economy as a way of preserving agricultural open space.

"We're losing the charm and the rural character rapidly," said Donna Rogers, who served on a citizens committee that proposed ways to preserve rural land. She thinks the Greenway accelerated development pressures already at play. "Every acre is being gobbled up. There's nothing being saved for farmland."

CAPTION: Growth Along the Greenway (This graphic was not available)