RICHMOND, FEB. 9 -- Baliles administration officials gave their blessing today to legislation that would allow a private company to build and operate for profit a 17-mile extension of the Dulles Toll Road from the airport to Leesburg.

Virginia Transportation Secretary Vivian E. Watts, appearing before a Senate subcommittee here, said the plan by New York-based Municipal Development Corp. could substantially speed construction of the road, which would be one of the first privately owned toll roads in the country.

"We support this bill," Watts said. "This gives us the vehicle to have . . . additional financing options that may get this road built significantly faster."

Lawmakers appeared to be reacting favorably to the proposal, which had been greeted with considerable skepticism when it was unveiled to the Governor's Commission on Transportation in the 21st Century last year. State and county officials initially were concerned that they would lack adequate control over the road, particularly in setting tolls.

"It has been a continual process" of revision, Watts said. "We think it is in good shape."

The toll road extension is considered critical to easing traffic congestion in eastern Loudoun County, home to Dulles International Airport and the scene of some of the most frenzied development activity in Northern Virginia.

Municipal Development Corp. claims to be able to complete the project in record time if the legislation is approved. Company officials released a proposed schedule today showing construction on the road beginning in late 1989 and concluding in late 1991, far sooner than under current state plans.

Although the fee for using the toll road has not been determined, company President John Miller said the toll "is clearly not $5. It's more in the range of a dollar." The company estimates the road would cost $125 million.

Under the proposal, the road would begin at the existing intersection of the Dulles Toll Road and Rte. 28, which skirts the eastern edge of the airport, then traverse the northeastern corner of the airport before angling north and west toward Leesburg. The road would connect with Rte. 15, also known as the Leesburg bypass, to the southeast of Leesburg.

The toll road bill, sponsored by state Sen. Charles Waddell (D-Loudoun), will be considered Thursday by the Senate Transportation Committee, which Waddell heads.

Under the legislation, the state and county would be given final say in how the road is built and how much people could be charged to drive on it. Both would essentially have veto power over the project if it did not evolve to their liking.

Moreover, Municipal Development Corp. officials said Monday that they had received assurances from the 20 landowners in the path of the road -- most with large holdings of commercially zoned property -- that they would donate the necessary right of way to allow the road to go through, presumably to improve development prospects for their property.

That commitment is important because it means the company could build the road without spending money on land. If the state were to build the road, landowners might choose not to donate their property for the road, knowing that the state would then have to condemn their land and pay them fair market value for it. The proposed legislation does not give MDC the right to condemn property to build the toll road.

Loudoun County Attorney Edward J. Finnegan, who attended the committee meeting, said in an interview that the county generally supports the idea of a private toll road.

In other developments today, the Senate Finance Committee unanimously approved legislation authorizing the state to issue revenue bonds to raise $160 million for the widening of Rte. 28 in Fairfax and Loudoun counties between I-66 and Rte. 7.