U.S. Transportation Secretary Ray LaHood said Wednesday that a meeting on Metro’s planned Silver Line to Dulles Airport yielded progress but not a final deal to move forward with the second and final phase of the $3 billion expansion.

LaHood, who mediated an earlier dispute over the fate of the project, called for the closed-door meeting of key officials in an effort to resolve a stalemate over a swirl of issues.

Virginia Transportation Secretary Sean T. Connaughton, chairmen of Loudoun and Fairfax counties’ boards of supervisors, and officials from Metro and the Metropolitan Washington Airports Authority joined LaHood for the meeting at his office in the District.

Some state and Loudoun politicians oppose what they view as a pro-union labor deal on the second phase’s construction, and they have pushed state officials to withhold $150 million from the project until the airports authority, which is overseeing construction, changes the incentive.

Loudoun supervisors also are worried about the project’s price tag. They have until July 4 to decide whether they will support the second phase. And some officials and interest groups are worried about the airports authority’s credibility: It is the subject of a federal investigation into contracting, governance and transparency.

Already, the bidding process for the second phase has been delayed.

LaHood said the incentive on the project labor agreement is a “sticking point” for Virginia and Loudoun officials. He said he plans to call a meeting with the airports authority and Virginia officials to “work out the project labor issue to the satisfaction” of both. That, some observers say, could prove to be a hurdle, given that neither side has shown a willingness to compromise.

Still, LaHood said after Wednesday’s meeting that he had “every confidence that this project will move forward.”

“Everybody believes this project is of regional and national significance,” he said. “There’s determination for it to move forward.”

Last fall, LaHood stepped in to help negotiate a financing deal for the second phase of the project.

The Silver Line’s first phase, which runs through Tysons Corner to Wiehle Avenue, is under construction and expected to be completed in August 2013. The second phase is expected to run from Reston to Dulles International Airport and farther into Loudoun.