Just a few hundred yards from the Metro station where the $5.6 billion Dulles rail line would end if the project’s second phase falls through, U.S. Senate candidate Tim Kaine (D) told business leaders Friday that the Silver Line must reach the airport for the sake of the region, the state and the nation.

The rail line will improve traffic and quality of life for thousands of Northern Virginians, Kaine said. It will also improve the standing of Dulles International Airport, which he described as one of two crucial economic resources, along with the Port of Virginia, that the Commonwealth is fortunate enough to possess.

“Every governor would love to have an international port,” he said. “Every governor would love to have an international airport. Most governors don’t get either of those things, and some governors might get one. But for Virginia to have both is just unheard of, and it’s one of the reasons the Virginia economy has outpaced other economies in a world where global connections matter more and more every day.”

Kaine, the former governor who helped push the project through along with a bipartisan team of Virginia congressmen, took few partisan shots as he made his case.

Kaine credited the Bush administration, particularly the former transportation secretary, Mary Peters, for its role in awarding more than $900 million in federal aid for the project’s first phase. He even complimented his opponent in this year’s hotly contested Senate race, Republican George Allen, for his support of the project when he was in the Senate.

“That’s bipartisanship,” Kaine told a gathering of the Greater Reston Chamber of Commerce. “As challenging as that was, we made it happen, and there’s no reason we can’t make sure Phase Two happens too.”

Kaine’s comments come at a time when the second phase is in jeopardy, with the Loudoun County Board of Supervisors contemplating voting against participating in the construction of the line’s final two stations. A “no” vote from Loudoun at the very least would delay the project; some boosters believe such a vote could sink the entire second phase, meaning the Silver Line would end at Wiehle Avenue in Reston and not make it to the Dulles airport. Loudoun must vote by July.

Kaine spoke close to the Wiehle Avenue station, which is under construction.

Kaine made one argument in favor of Dulles rail that carried a veiled partisan tone, arguing that the current tendency of politicians to neglect infrastructure investment is a big mistake.

“I see an anti-investment, anti-infrastructure mentality that has crept into politics,” he said. Kaine also weighed in on the sticking point for Loudoun County’s support of the project’s second phase, which is a labor agreement that opponents say is more pro-labor than the language of the Phase One agreement. Kaine said Friday that he thinks the language of the Phase One contract appears to be working — putting himself at odds with at least one member of the Metropolitan Airports Authority, Dennis Martire, whom Kaine appointed while governor. MWAA is the governing body overseeing the rail project.

That fact was not lost on Republicans, who issued a statement Friday about Kaine’s appearance accusing the candidate of bearing responsibility for the project’s cost overruns and “mismanagement.”

“Will Tim Kaine call upon his appointee and other board members to comply with Virginia law, which requires that Virginia workers get to compete for jobs on a level playing field?” asked state Del. Barbara Comstock (R-Fairfax) in a statement issued by the state Republican Party. “Or will he stick with his union cronies and biggest fundraisers, who want to leave Virginians with higher taxes and higher tolls while sending more of our jobs to Maryland and D.C.?”

Kaine said he would consider it a huge priority if elected to the Senate to see the rail project through.

“I sweated blood with others to make Phase One happen, and the fact that it’s being built on time and on budget makes me feel very, very good,” he said. “There are challenges and twists and turns and controversies, and there will be more.”