Fairfax County’s Board of Supervisors on Tuesday reaffirmed its commitment to extending Metrorail’s new Silver Line to Dulles International Airport and into Loudoun County, despite expressing concern about how the approximately $2.7 billion project will be funded.

File photo of the construction scene at the Dulles Airport Metro extension project (also known as the Silver Line) near the intersection of Rt 7 and Spring Hill Rd in the Tysons Corner area of McLean on Nov. 23, 2011. (Tracy A. Woodward/The Washington Post)

“It’s about the future,” Supervisor Penelope A. Gross (D-Mason) said. Next up is Loudoun County, whose board could back out of the project because of its cost and a dispute over the role of unionized labor on the project.

Under the management of the Metropolitan Washington Airports Authority, the roughly $2.8 billion first phase of the Silver Line is under construction through Tysons Corner to Reston. The first phase is expected to be completed next year. Construction of the second phase to extend the line from Wiehle Avenue to Ashburn is expected to begin in January. But conflicts about the project’s costs and how they will be shared has created turmoil over the past year.

Under an agreement brokered by U.S. Transportation Secretary Ray LaHood, the second phase would require Loudoun and Fairfax counties to foot the bill for construction of five parking garages and a Route 28 rail station. Fairfax County’s commitment would cost up to $498 million.

The county’s share for both phases will be about $900 million or more, about 80 percent of which will be borne by special tax districts in the corridor. That leaves a balance of at least $170 million that the board agreed to finance using using property taxes on commercial and industrial properties and other sources

Supervisor John C. Cook (R-Braddock), noting that the state may withhold at least $150 million if the airports authority insists on giving preference for organized labor on the project, urged the board to make its approval contingent on the authority removing its preference for a project labor agreement. His amendment failed.

Some members voted for approval despite reservations about its costs, saying the project was too far along and too important for economic development to stop now.

“What a long strange trip it’s been,” said Supervisor Michael R. Frey (R-Sully), quoting a song line from The Grateful Dead. “To be honest, I come up with far more reasons why we shouldn’t, than for why we should.”

But Frey also said the project was never designed to terminate at Wiehle Avenue.

But Supervisor Jeffrey C. McKay said the board had to take the long view, saying the Metrorail project would prove to be as critical for the region’s economy as the construction of the airport was decades ago.

“This is Fairfax County’s economic engine, but it’s also the state’s,” McKay said. He pointed out that the project would proceed regardless, with the only open question whether expected increases on toll road users would be moderated by state aid or other sources.

Supervisor Patrick S. Herrity (R-Springfield), who recently underwent open-heart surgery, was absent for Tuesday’s meeting. Loudoun now has until July to reach a decision.

Jim Corcoran, president and chief executive of the Fairfax County Chamber of Commerce, praised the board’s action as an important step toward making sure the region’s economy remains strong. He also called on the Commonwealth to boost its contribution to the project and urged the airports authority to drop its stated preference for a project labor agreement.

“As the work continues in the months ahead, the Chamber remains a strong advocate for the timely and cost effective completion of this critical project,” he said in a written statement.

After making some last-minute tweaks, the board also agreed on names for eight stations in the county and forwarded those to the Washington Metropolitan Area Transit Authority’s board for approval.

The names, which were recommended by staff after receiving suggestions from the public at several meetings and an online survey, are: McLean (1824 Dolley Madison Boulevard); Tysons Corner (1943 Chain Bridge Road); Greensboro (8305 Leesburg Pike); Spring Hill (1576 Spring Hill Road) ; Wiehle-Reston East (1862 Wiehle Avenue, Reston); Reston Town Center (at the intersection of Route 267 and Reston Parkway); Herndon (at the intersection of Route 267 and Monroe Street); and Innovation Center (at the intersection of Route 267, Route 28 and Innovation Avenue).