The promise was made not once, not twice, but seven times by Republican gubernatorial candidate Jerry W. Kilgore.

"I'll widen I-66 inside the Beltway," he said during the Sept. 13 debate with his Democratic opponent, Timothy M. Kaine, sponsored by the Fairfax County Chamber of Commerce.

It's a pledge the GOP candidate has embraced boldly. In television ads, speeches and interviews, Kilgore has said that one of Northern Virginia's most controversial proposals -- the widening of four-lane Interstate 66 in Arlington County to six lanes -- can be done with a bit of political will and the efficient use of federal money.

But completing a project that has been repeatedly proposed, discussed and postponed since that 10-mile stretch of I-66 opened in 1982 would be a daunting task for Kilgore.

Costs and community opposition make it difficult for any local leaders to advance a major transportation proposal. In Maryland, Gov. Robert L. Ehrlich Jr. (R), who set construction of the intercounty connector as a major goal during his 2002 campaign, still hopes to begin building before the end of his term.

The Arlington communities along the I-66 route have long been concerned about noise, air pollution and traffic congestion associated with the highway. The Arlington County Board, which tried to block construction in the first place, continues to oppose any widening.

"If the widening occurs, it will be over the objections of the local community," said Jay Fisette (D) chairman of the County Board, which passed a resolution in the spring reaffirming its opposition.

Although county officials would not have final say on a state project, opponents would be able to testify at hearings held by state agencies weighing community interests.

"We understand local concerns, but this is a regional project," said J. Tucker Martin, a spokesman for Kilgore. "This would be for the good of the region and is a priority for Jerry Kilgore."

Kilgore says the two-way widening can be accomplished within the existing right of way, without taking any property.

Under his plan, a 6.5-mile stretch from the Rosslyn tunnel to the Dulles Connector Road would be widened first. Kilgore says the state then should study the feasibility of widening the road through the Rosslyn tunnel and across the Theodore Roosevelt Bridge into Washington.

According to Virginia Department of Transportation officials and other planners, Kilgore is correct in asserting that the road can be widened to six lanes without taking private property and within the existing right of way.

Sound walls, fiber-optic cables and utilities would have to be moved, and drainage would have to be upgraded. A biking and walking trail along the interstate also would have to be adjusted.

The widening would be further complicated if two shoulders were included, one in each direction. Kilgore's campaign said it has not determined whether the plan would include shoulders, but VDOT officials and transportation experts said such an improvement should be included for safety reasons.

Although Kilgore wants to widen the highway in both directions, he has outlined how to pay for the eastbound lane only.

"The cost of this project is estimated at approximately $160 million," the Kilgore plan says, although campaign officials said the price tag might increase to $193 million.

The estimate is based on "preliminary numbers" from VDOT, according to the campaign.

Joan Morris, a spokeswoman for the agency, said that widening the westbound side would probably cost $112 million to $233 million but that VDOT does not have a cost estimate for widening the interstate in the eastbound direction.

VDOT officials speculate privately that widening the road in both directions would cost $224 million to $466 million, depending on the scope of the project.

The campaign said Kilgore would earmark $40 million a year in federal funds for the project, as well as an additional $33 million in other federal highway money, to reach the $193 million figure.

Asked how Kilgore might make up a difference that could range from $31 million to $273 million, Martin said: "We believe we'll be able to draw down federal dollars to complete the project. It's hard to give specific numbers when you're not in office."

Federal and state statistics show that new highway money from Congress over the next several years will probably range from $92 million to $105 million per year. However, congressionally earmarked projects take up a minimum of $50 million annually, records show.

That leaves $42 million to $55 million a year for all other projects where federal funds are needed, including extra money for widening I-66, according to VDOT officials.