AT MIDDAY ON WEDNESDAY, just over a dozen politicians and officials, mostly Virginians, will troop into Transportation Secretary Ray LaHood’s office, hoping to rescue Metro’s Silver Line extension to Dulles International Airport. What’s at stake is one of the largest public infrastructure projects in the country, now in jeopardy of coming unraveled in an increasingly bitter feud over costs and financing. Mr. LaHood, having recently rescued another major project , the modernization of Chicago’s O’Hare International Airport, from a similarly venomous impasse, has offered to mediate.

That’s a promising sign, and not just because of Mr. LaHood’s deftness as a go-between. Just as important, he has a critical say in the disposition of federal transportation loans, which could be the key to resolving the Silver Line standoff.

On one side is the Metropolitan Washington Airports Authority board, which controls the Silver Line project as well as the Dulles Toll Road. Revenue from the toll road is to provide three-quarters of the funding for the project’s second stage of construction, running from Reston through the airport and west into Loudoun County. On the other side are virtually all the project’s other stakeholders — local officials and congressmen from Northern Virginia; Virginia’s transportation secretary; and Metro itself, which will operate the Silver Line once it’s built.

The fight has been billed as one involving the location of the future Metro station at Dulles. In fact, this is a dispute about cost. Specifically, it is about whether the airports authority board, an unelected body, can blithely spend billions of dollars in public funds with no regard for fiscal constraints and the legitimate concerns of commuters whose toll rates may triple or quadruple as a result of its actions.

That blithe disregard was evident in the board’s 9 to 4 vote this spring in favor of an underground station at the airport, where an aboveground one would sacrifice very little in terms of design or convenience — and save $330 million. The cost of an underground station represents just 5 percent of the Silver Line’s overall $6 billion price tag. But it is just the latest example, and now a symbol, of the repeated upward cost revisions of the project, which has almost doubled in price since 2004.

In this case, it was one revision too many. Thousands of toll road users are facing soaring increases in the cost of their daily commute to finance the Silver Line’s construction. They deserve to know that the project is being built and managed as cost-efficiently as possible.

Additional savings could certainly be found. Possibly, plans for a Metro rail yard at Dulles could be scaled back, at a savings of tens of millions of dollars. Plausibly, Metro’s construction standards, devised during the Cold War to withstand nuclear attack, could be revised. Maybe nips and tucks on parking, station canopies and the like could account for other reductions in cost. But ditching the underground station at the airport would save more.

Mr. LaHood wields the power of the purse; without some federal help for the project’s second leg, it’s increasingly likely that the deal may fall apart. He should use that clout to promote cost controls and exact concessions from the airports board, whose majority has stuck to its politically tone-deaf, fiscally reckless stance.