Both political parties sought to capitalize yesterday on Northern Virginia's mounting exasperation with traffic, holding dueling news conferences that underscored the prominence of transportation as a campaign issue.

Days before Tuesday's state elections, Gov. James S. Gilmore III (R) and Rep. Frank R. Wolf (R-Va.) promoted their plans to alleviate congestion, in particular their initiative to widen Interstate 66 inside the Capital Beltway. They repeated their determination to add a third lane in either direction despite opposition from Arlington County officials, who say this would violate a 1977 agreement limiting the highway to two lanes each way.

Hours later, Democratic legislative candidates opened fire on the Gilmore administration for recent revisions in the state's highway blueprint showing that the reconstruction of the Springfield interchange is officially scheduled to take at least 9 1/2 years--not eight as state officials earlier promised. Gilmore and other state transportation officials have said they remain committed to finishing it in eight years and will do so by accelerating future phases of the project.

Democratic candidates, rejecting these assurances, called on the General Assembly's auditing arm to investigate the state's management of the interchange construction, the most ambitious highway project in the region.

Speaking at the Virginia Department of Transportation offices in Springfield, the Democrats took repeated swipes at Gilmore and his Republican predecessor, George Allen. They accused the two governors of leaving VDOT without the staff and funds to complete the project on time.

"I don't think anyone knows for sure what's going on at VDOT," said state Sen. Janet D. Howell (D-Fairfax). "The governor says one thing. Official VDOT documents say another."

At the earlier Republican news conference, held in an Arlington parking lot overlooking I-66, Gilmore and Wolf pressed their plans to ease traffic congestion by extending Metrorail in the Dulles corridor, encouraging telecommuting and widening the interstate.

The effort to add lanes to I-66 inside the Beltway was jeered by about 20 protesters. But the governor persisted, saying this was a vital part of his statewide transportation plan unveiled in August. "It's about time. It's long overdue, and I'm proud to be leading the charge on this," he said.

Wolf, who won federal legislation this month voiding the compromise that banned more lanes, said rapid development in Northern Virginia made changes on I-66 necessary. "Things have changed," Wolf said.

CAPTION: Above, Caroline George, 10 months, accompanies her parents to a demonstration opposing the widening of Interstate 66. Left, Gov. James S. Gilmore III, center, holds a news conference in Arlington on the widening. With him are, from left, Del. Roger J. McClure, Rep. Frank R. Wolf, Del. Vincent F. Callahan Jr. and Shirley Ybarra, transportation secretary. Behind them are the protesters' signs.