RICHMOND, MARCH 2 -- The Virginia General Assembly, setting the stage for a development explosion on the western fringes of the Washington area, approved and sent to Gov. Gerald L. Baliles today legislation that would permit a private partnership to build and operate a for-profit extension of the Dulles Toll Road to Leesburg.

Baliles has said he will sign the bill, which lifts a three-decade-old ban on private toll roads in Virginia and provides a testing ground for assertions that the private sector can build the 17-mile, $100 million road faster and cheaper than the state.

Transportation officials say the road will meet a "desperate need" to unclog traffic in Loudoun County's prime development corridor, just west of Dulles International Airport. But if the private developers receive the necessary approvals from state and local agencies, the road project could touch off a high-stakes game of real estate roulette that may have less to do with providing better transportation than with piecing together an intricate puzzle of private property interests.

The shrewdest among the players, who include some of the Washington area's most powerful developers, will get proximity to the new road and perhaps even a nearby interchange -- prizes that will determine who gets rich, who gets richer and who gets richest in Northern Virginia's ripest development frontier.

The vote today in the state Senate, 36 to 1, came without debate; the House of Delegates approved the bill Monday.

Today's action represented a turnaround for financiers Municipal Development Corp. of New York and engineers Parsons Brinckerhoff Quade & Douglas of Fairfax County, whose proposal in November 1986 to build and operate the toll road without using tax revenues was roundly dismissed by state and local officials.

Critics said the plan seemed a departure from history and common sense: Private toll roads had gone the way of covered wagons, overrun by the nation's burgeoning interstate road system, which democratized the highways by making cross-country travel on good roads accessible to rich and poor alike.

Northern Virginia developer and lawyer John T. (Til) Hazel Jr. argued that if a private firm could make a profit on the toll road, then the state -- the traditional road-builder in Virginia -- could do the same job at less cost.

But the legislation gathered steam, propelled by the blandishments of one of the state's most powerful lobbyists, Alexandria attorney William G. Thomas, and support from the governor and key state officials. Northern Virginia lawmakers, all of whom promised in their reelection campaigns last fall to attack traffic congestion and build new roads, added momentum.

As for Hazel, not only did he reverse his early opinion after Thomas, his law partner, became involved, but he and his brother purchased hundreds of acres of land along the road's proposed alignment.

Despite the impressions of many who supported the measure, the private sector plan to build the extension from Dulles northwest to Leesburg is not home free. Although the development firms convinced many lawmakers that they can build the road quicker and cheaper than the state can -- and without tax revenues -- the real challenge will be to negotiate the road's precise alignment, according to several property owners in the corridor.

"A lot of companies want the exposure to the highway traffic," said Bob Buchanan, a developer who has been active in land use matters in the Dulles area. "It definitely will have a positive effect on the value of the property to be located on the road."

The corridor where the road would go, roughly parallel to Rte. 7 and the Potomac River, is now largely rural. Some parcels are the site of weekend fox hunts. But a handful of huge development projects are already under way, and county plans envision dozens of low-rise office buildings, warehouses and distribution centers as well as thousand of houses, town houses and apartments. The extension of the toll road is expected to supercharge the area's growth.

Construction could start early next year and be finished by the end of 1991, according to the developers.

The coming scramble for real estate profits has rankled a few critics, including state Sen. Dudley J. (Buzz) Emick Jr., a Democrat from southwest Virginia who cast the only dissenting vote today when legislation to permit the private toll road passed the state Senate.

"I resent the implication that this is being done in the name of the public good," said Emick. "The principal landowners who will route the road and provide access to it are the ones who will benefit enormously."

Judging from the jockeying for position already in progress among property owners, Emick may be at least partly correct. At least two engineering firms have been retained by groups of landowners to devise possible alignments for the road that would best serve their land interests while satisfying engineering and environmental requirements. A consultant hired by the state has drafted several other possible alignments. And, the would-be developers of the road, Municipal Development and Parsons Brinckerhoff, have drafted a few.

Although the half dozen or so proposed alignments for the road appear to take similar paths across a map, those curves and squiggles, landowners say, can make the difference between mere success and huge profits for a given parcel's development.

One landowner, Reliance Development Group of New York, has criticized one alignment proposed by the prospective road's developers. The alignment, which skirts the Reliance property to the south, missing it by less than a mile, is inequitable, according to Stewart J. Gerson, Reliance's assistant vice president.

"The interests of the landowners should be served," Gerson said. "They're the ones who are going to be bringing in the tax revenue by their developments."

Officials for Loudoun County, which would be a beneficiary of those tax revenue, warn they will veto any alignment that serves private rather than public interests.

"It will not be developers who determine the alignment," said county attorney Edward J. Finnegan. "It will be the {Virginia} department of transportation along with the county and the town" of Leesburg.

William H. Allen, regional manager of Parsons Brinckerhoff, acknowledged that if his company helps develop the road, "that doesn't mean the best alignment for specific property owners . . . .

"There's a public interest we have to meet and we're going to meet it."

It is by no means certain that the state will forfeit its traditional role as road-builder to the private developers who want to build the Dulles toll road extension.

The developers must first receive approvals from the state's Department of Transportation as well as the State Corporation Commission.

If they get the go-ahead, however, they would still lack a fundamental tool of road-building wielded by all states: the power of eminent domain, which allows states to seize private property for public purposes, as long as they compensate the owners.

Municipal Development Corp. and Parsons Brinckerhoff have said they have no funds set aside to purchase land for the road's construction. Rather, they say, they are counting on land donations by property owners who are eager to have the road finished as quickly as possible.

The developers' dependence on donations of land may make the process more beholden to the whims and pressures of private landowners than it would be under state control. "If we can't satisfy the development needs of the landowners, we can't build the road," said John D. Miller, president of Municipal Development.

Thomas, the lobbyist who shepherded through the legislature the bill that would allow the road to be privately built, told lawmakers last week that the 20 property owners in the corridor had all written letters expressing their willingness to donate the necessary 250-foot ribbon of land through their properties for the road.

Despite Thomas' assurances, a survey of property owners in the corridor shows that the commitments to donate land are not as firm as he suggested. In many cases, landowners have made no promises at all.

"We said we'd work with them, but that doesn't mean it's going to be a gift" of land, said Alan I. Kay, who owns more than 200 acres near Leesburg. "We have not agreed that we would shoot ourselves in the foot."

Another landowner, who asked not to be identified, said: "Let them make me an offer. Put me near an interchange, or whatever. They haven't put any specifics to me yet."

Asked about the apparent discrepancy, Thomas said he had been repeating information supplied by Parsons Brinckerhoff. "I don't think they're telling stories," he said, adding, "If the land isn't donated, this project can't go anywhere . . . . There's an incentive for the landowners to be cooperative."

Thomas seems ideally situated to act as a broker among the competing interests likely to be involved in the road's construction, although he says that conflict-of-interest considerations prevent him from doing so.

An influential lobbyist, he guided the legislation on behalf of Municipal Development and Parsons Brinckerhoff through more than a dozen drafts. His law firm has done zoning work for four of the major landowners along the toll road corridor in Loudoun, and he has personally handled two of those clients.

In addition, his law partner Hazel, as well as Hazel's brother William, is a major property holder in the corridor. Thomas also sits on the board of the airports authority, which would have to approve the route taken by the toll road as it crosses Dulles property.

Despite his assortment of roles, Thomas says he has not been involved with the sensitive issue of road alignments. In the disclosure forms he is required to file as a Richmond lobbyist, he lists among his clients Municipal Development and Parsons Brinckerhoff but not his property-owning clients in Loudoun who might benefit from one or another alignment. "I have avoided any kind of a brokerage role," he said.

Nonetheless, there have been some concerns -- expressed privately and on condition of anonymity -- that the property owners who Thomas represents, including developer Glen T. Urquhart and Van Metre Land Corporation, may have a leg up in the alignment game.

"You can't tell whether the maps show the road going through Urquhart's property for reasons of fairness and good engineering or for reasons of influence," said one source close to the process who asked not to be identified.

Urquhart, who has plans to build office buildings, warehouses, apartment buildings and a hotel on his 543 acres, said he purchased his property more than four years ago based on an "informed judgment" that it was the logical place for the road to go.

ROYCO INC. -- Alan I. Kay: Two parcels: Total 242 acres. Intended use: office, industrial space, 1,000 or more dwelling units.

ASHBURNS FARMS -- William A. Hazel, John D. Stokely Jr.: 1,274 acres. 1,724 single-family homes, 1,340 town houses, 766 apartments, two shopping centers with 225,000 square feet of retail space, 75,000-square-foot office park, high school, elementary school, library, four churches, three day care centers, three recreation sites.

BROADLANDS -- Van Metre Land Corp.: 911 acres. 1,076 single-family homes, 722 town houses, 317 garden apartments, 1.7 million square feet of office space, 58,000 square feet of retail space, 272,000-square-foot mixed use (retail and medical offices,) one middle school, one elementary school.

SOUTHMARK CORP. -- John T. "Til" Hazel, William A. Hazel, John D. Stokely Jr.: 542 acres. Intended use: office, industrial space. 800 to 900 dwelling units.

GLENWOOD -- Glen T. Urquhart: 543 acres. Intended use: 5.9 million square feet of office space, warehouses, shops, distribution centers. Also: hotel, 990 apartments, day care for children, elderly.

RELIANCE DEVELOPMENT GROUP -- 308 acres.