After months of haggling, state officials and Northern Virginia developers have reached a tentative accord on how to finance the widening of Rte. 28, a $300 million project deemed crucial to continued economic growth in Fairfax and Loudoun counties.

In May, some developers along Rte. 28 threatened to withdraw their support for a proposed transportation tax district, a novel plan under which they would be assessed extra property taxes to help pay for the 15-mile widening project. The landowners complained that the state was not contributing enough money to the undertaking.

According to developers and state officials, however, those differences have been largely resolved, with both sides agreeing that the developers will contribute the bulk of the money for the project.

"I don't think we have it all sewed up yet, but there is a meeting of the minds," said Francis Steinbauer, senior vice president of the Henry Long Co. in Fairfax. Steinbauer is a member of the committee of public officials and developers that is thrashing out the details of the financing plan.

Now a two-lane road, Rte. 28 has become one of the busiest in the region because of development in the vicinity of Dulles International Airport. Long-range plans call for widening it to an eight-lane freeway with 13 major interchanges between I-66 and Rte. 7 in Loudoun County.

For now, however, the state is planning to widen the same stretch to six lanes with three new interchanges, a four-year project that would cost about $130 million and could begin as early as next spring, according to Virginia Transportation Secretary Vivian Watts.

"We'd be lucky to see it 20 years from now" without the developers' contribution, Watts said.

While both sides are optimistic that the major problems have been resolved, significant differences remain. For example, while Watts said yesterday that the developers had agreed to finance 80 percent of the project, Steinbauer said that 75 percent was "our bottom line."

In addition, some developers have stipulated that they will not support the tax district unless the state commits itself to completing the entire project with all eight lanes, according to Fairfax Deputy County Executive Denton U. Kent. Moreover, Kent said, some Fairfax County politicians are concerned that Watts' plan will siphon off money from badly needed road projects in their districts. He added, however, "I do think this is a step in the right direction."

Under the tax district law passed by the General Assembly in its last session, Fairfax and Loudoun counties can assess an extra 20 cents on the dollar on property taxes from commercial landowners along the Rte. 28 corridor. Before the tax district can be implemented, however, 51 percent of the landowners must agree to it.

Money from the tax district would be used to finance the $130 million bond issue for the first phase of the project, which would ultimately cost about $200 million when interest is factored in, according to Watts. She said the state had agreed to pay $40 million, or about 20 percent of the cost.

Steinbauer, the developers' representative, noted that the developers originally sought a 50-50 split with the state. "As in all things of this nature, everyone has moved some," he said.