Fairfax County Board Chairman John F. Herrity, entering the final week of a tough reelection campaign, unveiled a plan yesterday that he said could solve some of the major transportation problems his chief opponent accuses him of creating.

After accepting endorsements from several of Virginia's leading Republican politicians at an afternoon news conference, Herrity announced that four major developers had agreed to consider creating a special tax district to pay for transportation improvements in the Tysons Corner area and possibly along the corridor between Dulles International Airport and the West Falls Church Metro station.

However, the plan, which Herrity said could be worth "$100 million in the bank," resolves no particulars and its backers emphasize that it is far from fruition.

Under the tax district, similar to that being created to finance the widening of Rte. 28, commercial and industrial landowners would pay higher taxes to pay for the improvements. The proposed improvements include widening Rte. 123 and Rte. 7 and extending mass transit in the Dulles corridor.

The four developers, whose holdings of more than half of the commercial property in the area entitle them to petition for a tax district under state law, are Charles Ewing of the West Group, E. Wayne Angle of H-L Land Improvement Venture, Charles Cope of Tysons Corner Center, and James T. Lewis of J.T.L. Tycon Developers.

Herrity called their commitment to negotiate with one another and the county during the next six months a historic achievement, although no agreement has been reached on the projects to be undertaken, the amount to be raised or the rate at which commercial property would be taxed.

"This is really pretty preliminary," said Ewing. "We haven't agreed to anything except to bring this possibility to the county's attention and discuss it."

Angle said his willingness to form a tax district is conditional on the government agreeing to credit him for money he has already spent on road improvements in the area. Angle, whose venture has spent about $15 million, said he did not know whether he would pay additional taxes under such an arrangement.

If the developers can reach an overall agreement, they would petition the county to hold a public hearing. Supporters of the plan, which would affect only commercial property, would then petition the Circuit Court to create the tax district.

The General Assembly would have to approve any plan that does not treat all commercial taxpayers within a tax district equally, according to Shiva Pant, director of the county transportation office.

Herrity's opponent, Democratic Supervisor Audrey Moore, praised the idea of developers subsidizing improvements but said the developers agreed to the announcement to give the chairman a political boost.

"I think this is being announced at this time because these particular developers are interested in helping Mr. Herrity win the election," said Moore, who holds a lead in the polls.

The proposed Tysons area transportation tax district would not be sufficient to finance mass transit for the entire 16-mile Dulles corridor, but might be the first in "a series of tax districts" along the route that might serve as "a lever for state funding" of any project, Herrity said.

Virginia Transportation Secretary Vivian E. Watts said her office had not been consulted on the Herrity proposal, but said "a lot will need to be looked at" before it can be considered "a done deal."

The state legislature would have to approve issuing state bonds if they are needed to pay for initial construction costs, Watts said.

Any additional state financing "comes out of other Northern Virginia projects," Watts said. Legislators from other parts of the state "are not about to let Northern Virginia set the priorities for the rest of the state's road needs," she added.