Two years into a torturous planning process, the private firm that expects to extend the Dulles Toll Road from the airport to Leesburg hopes to break ground within six months and finish work by mid-1993.

That estimate, more than a year behind early schedules, depends in large part upon the U.S. Army Corps of Engineers and the financial market, said Toll Road Corp. of Virginia President Ralph L. Stanley. The Corps of Engineers must issue a permit authorizing the use of wetlands, and Stanley said his firm can't close the deal providing the highway's construction money until the permit and other loose ends are tied up. His company recently submitted a five-volume application to the Corps of Engineers, but it's unclear how long it will take to process the request for a permit.

Such reviews can take "30 days or six months, depending on the parameters of the individual application," said William Brown, a spokesman for the Corps of Engineers in Virginia.

Finding investors may be no small accomplishment in the current economic slowdown. Stanley said his firm will be promoting the toll road project actively before the Corps acts so that the money can be obtained shortly after a wetlands permit is issued.

"Groundbreaking could occur immediately" after those actions, said Stanley, a former chief of the Urban Mass Transportation Administration, whose toll road company is based in Leesburg.

In addition, state transportation officials have yet to sign off on late adjustments to interchange designs. Virginia's Commonwealth Transportation Board and State Corporation Commission have given conceptual approval to the private toll road, the first authorized in Virginia since 1816.

And the Metropolitan Washington Airports Authority has not yet amended its master plan for Dulles to let Stanley's firm build on the northern part of the airport property.

Airports Authority officials say that this action could come as early as February. But a lawsuit challenging the constitutionality of part of the law under which the Airports Authority operates has left a legal cloud over all major actions of the authority.

The issue may not be resolved in the courts or Congress within six months, say some lawyers involved with the case.

All private landowners along the proposed 15-mile toll road extension have agreed to donate or sell land for the right of way.

The state operates the existing 15 miles of toll road between Interstate 66 and Route 28 near the airport; the government's profit on the highway is approaching $10 million a year, officials say.

The new road, which would have an initial toll of $1.50 between Route 28 and the Leesburg Bypass (Routes 7 and 15), will stimulate residential and commercial growth in a largely rural strip of Loudoun and will give commuting workers a break from Route 7.

Some Loudoun County government officials and environmentalists have expressed concern about the potential increase in population, in part because new people need schools, emergency services and feeder roads at great cost to the county government.

Some officials also have expressed concern that any additional delays in the toll road extension could slow the kind of commercial development that adds more tax dollars to the county government's treasury than it costs.

"I'm very concerned that {the road project} is going to founder" because of the lengthy Corps of Engineers review process and the tight financial market, said County Board of Supervisors Vice Chairman Charles A. Bos (D-Leesburg). Bos said he and other county officials strongly support the private firm's plans.

As much as 40 acres of wetlands may be subject to the Corps of Engineers review, officials say.

Corps spokesman Brown said his agency looks first to see whether using wetlands can be avoided. Next, the agency tries to find ways to mitigate disturbance of such property.

If those options are not practical and the use of wetlands is deemed essential to the public, the Corps determines appropriate compensation for wetlands loss, Brown said.

Stanley said his firm has budgeted $1 million to replace wetlands by purchasing natural areas elsewhere in Loudoun. In some cases, he said, the company will replace forested wetlands with more acreage than the road takes.