RICHMOND, FEB. 24 -- The latest innovative financing proposal to accelerate the widening of traffic-clogged Rte. 28 near Dulles International Airport passed its final legislative hurdle today.

By a vote of 88 to 8, the House of Delegates approved a bill that provides three levels of guarantees for state revenue bonds that will be sold to help finance the $123 million project. The project will run for 14 miles, between I-66 and Rte. 7, and will transform the present two-lane road into a six-lane, divided expressway with three interchanges.

Transportation Secretary Vivian E. Watts said the measure should allow construction to begin within a year, probably in the fall. The work will take about three years, she said.

The proposal met some opposition because it was amended in the Senate to include, as a third level of guaranteeing the revenue bonds, the full highway department trust fund.

The primary source for paying off the bonds will be a special tax of 20 cents on each $100 of assessed value imposed on the owners of about 500 acres of valuable commercial property bordering the 14-mile expressway in Loudoun and Fairfax counties.

Watts said the special taxing district will produce about 80 percent of the cost of the construction, with the remaining 20 percent to be paid from regular transporation department funds designated for Northern Virginia road projects. Watts said the special financing "won't change a single project" in Northern Virginia.

Opponents worried that using the state trust fund as collateral for the bonds would detract from the ability of other areas of the state to tap into the fund, or set a precedent in which other regions would adopt such financing.

Del. C. Richard Cranwell (D-Vinton), the chief sponsor of the bill in the House, said the only way other areas could qualify for such treatment would be to come up with similar local tax support.

The "risk is nonexistent" in adding trust funds as a backup, Cranwell said.

The Senate tacked on the trust fund requirement after bond lawyers said a third level of guarantee would result in selling the bonds at a lower interest rate, which would benefit all state bonds.

Cranwell, who represents a district in the Roanoke area, urged legislators from outside Northern Virginia to support the proposal "because we are a unified state, with unique problems."

Gov. Gerald L. Baliles proposed the legislation after the Virginia Supreme Court ruled last fall that the sale of pledge bonds was unconstitutional. The pledge bond plan, which would sell bonds to be paid off by gasoline taxes and other highway revenues, was authorized in the September 1986 special session of the legislature.