Virginia officials gave final state approval yesterday to a private company's bid to extend the Dulles Toll Road from the international airport to Leesburg.

The 14-mile, $227 million project would be the nation's longest privately operated toll highway and would provide an outlet for growing traffic pressures west of the airport in one of the area's fastest growing commercial and residential corridors.

The decision by the State Corporation Commission removes the last regulatory hurdle for the project and comes nearly a year after the policy-making Commonwealth Transportation Board approved the proposal from the Toll Road Corp. of Virginia.

However, the company, which is designed to make a profit, must still obtain financing and routine permits and acquire some land for the extension. Company officials say they anticipate receiving financing this fall and expect little difficulty getting permits. The acquisition of right of way could be a tougher issue because the company cannot take land by condemnation the way a government is allowed to do.

The State Corporation Commission, which will regulate the highway's operation under a 1988 state law authorizing private toll roads, approved an initial toll of $1.50 for cars. The extension is targeted for opening in April 1993, more than a year behind original plans.

The toll would rise to $1.75 in January 1994 and $2 two years later. Higher charges will be permitted for trucks. Investors in the company will be eligible to receive up to 30 percent profit on some of the capital needed to finance the project.

The state currently charges 85 cents to travel the length of the existing, profitable 15-mile toll road, which connects the Capital Beltway with the airport and is being widened from four to six lanes. The total toll between the Beltway and Leesburg, avoiding the hassles of heavily choked Route 7, will start at $2.40, including a 5-cent increase in the state charge.

The commission's order ends a seesaw odyssey in a project without precedent in Virginia. An intense campaign by some staff members of the Virginia Department of Transportation to show that the state could build the extension faster and cheaper continued until this spring, according to some state legislators critical of the agency. Some commission staff members made similar suggestions in an initial report to the three-member commission.

However, state Transportation Secretary John G. Milliken helped smooth the way for the private firm's bid, according to Toll Road Corp. of Virginia Chairman Ralph L. Stanley, a former chief of the Urban Mass Transportation Administration.

"This is the happiest we've been in 19 months" since forming the toll road company, Stanley said yesterday.

The commission certificate blocks any effort by the state Department of Transportation to extend the highway and follows an official finding that the private firm's application meets the public interest. Since the Department of Transportation said recently that it has no money to build the extension, the private bid "is the only game in town," according to the commission's order.

Because Stanley's firm has no power to automatically take right of way, the company is negotiating with landowners and the Metropolitan Washington Airports Authority for the five miles it still needs. It has received agreements in principle to provide right of way from about 20 landowners -- including several major development firms -- in exchange for interchange rights or anticipated property value escalation.

The company is dependent on Milliken and other state transportation officials to conclude a complex deal that would free up the right of way on the airport property. The airports authority, which runs Dulles and National airports, wants a state commitment that excess revenue from the existing toll road will be committed for bus and possibly rail service to link Dulles with the Tysons Corner area and the Metro subway.

The project is the first private toll highway authorized in Virginia since 1816. Proposed at a time of severe strain on government road-funding budgets, the private extension was endorsed strongly by Gov. L. Douglas Wilder and his predecessor, Gerald L. Baliles.

Stanley and state officials have said the success of the Dulles Toll Road initiative could open the door for other big-ticket, private toll proposals in Virginia. Several projects in the Tidewater area and the widening of Interstate 66 outside the Capital Beltway have been mentioned as possibilities.