Ordinarily, I’d gladly support spending an extra $300 million to do the job right by putting the new Metro station at Dulles airport underground and closer to the terminal. Among other advantages, a below-ground station would last much longer than one perched on girders and exposed to the weather.

Moreover, as a rule, I’d happily support the plan to pay for the station by gouging drivers on the Dulles Toll Road. If there’s one thing the Washington region needs to do over time to solve our traffic problems, it’s to effectively tax passenger cars in order to improve mass transit.

However, I have concluded with wistful regret that the underground station, though laudable in theory, is doomed to defeat in practice. The uneasy alliance of Republicans and cost-averse Democrats that’s sprung up to demand a less-costly aerial station is too powerful to overcome.

As a result, the Metropolitan Washington Airports Authority needs to swallow its pride and reverse its recent choice of an underground station for Dulles on what’s known as the Silver Line. Otherwise, the plan to extend Metrorail service to the airport and beyond risks being sucked into a sinkhole of ugly political infighting that would threaten funding for the whole project.

The airports authority, which is in charge of building the rail extension, should signal its willingness to compromise as early as Wednesday, when Transportation Secretary Ray LaHood has called a top-level meeting of federal, state and local officials to start discussing a deal.

The airports authority has another strong motivation to back down: Politicians of both parties are losing confidence in it. That’s partly because of the controversial station decision, partly because other costs have risen sharply from original estimates, and partly because the authority has been without a permanent chief executive for a year.

It’s getting so bad that the airports authority is challenging the Metro transit board for the title of most dysfunctional transportation body in the region.

“Part of a deal has to be permanent, stable leadership at the airports authority,” said a high-ranking official close to the deliberations, who spoke the condition of anonymity because of the sensitivity of the issue. Such leadership is required so the airports authority “can make and keep a deal with Northern Virginia authorities, both congressional and local,” the official said.

It’s crucial that Northern Virginia keep the Silver Line moving forward. Much more is at stake than convenience at the airport. The underlying issue is finishing the work of providing quality rail service through some of our area’s richest, fastest-growing communities in western Fairfax and Loudoun counties.

Pique over the more costly station has prompted Loudoun to make noises about not paying its share of the second phase of the project, which would extend the line to six additional stations, including Dulles. (Phase one, through Tysons Corner, is under construction.)

The rest of the bipartisan group demanding savings includes the state administration in Richmond, Virginia Reps. Frank R. Wolf (R) and Gerald E. Connolly (D), and Fairfax County Board of Supervisors Chairman Sharon Bulova (D).

Even though Dulles Toll Road tolls are paying for most of the rail project, the local governments have considerable leverage because their support is necessary to obtain critical federal loan subsidies.

“Once you stall, once you have something creating some discord, things can unravel pretty easily, and it’s hard to pull things back together again,” Bulova said.

The issue is especially politically sensitive for Democrats in a swing county like Fairfax , who are vulnerable to GOP accusations that they’re overspending. Bulova is up for reelection in November, and Connolly faces the voters next year.

The criticism has frustrated members of the airports authority board who say the extra cost is worth it to place the station 600 feet closer to the terminal.

“I feel like I’m being bullied by the state, and I’m being bullied by the [funding] partners. I’m doing it for the families that have to use Metro, for the single parent that’s traveling internationally, and has three pieces of luggage and two kids in hand,” said Mame Reiley, an airports authority board member who is the leading advocate for an underground station.

Reiley and her allies also point to financial analyses concluding that the extra cost of the underground station is such a small part of the total bill that it would account for an average of only about 50 cents of the one-way toll on the Dulles Toll Road.

The problem with that argument is that the tolls are going to soar, regardless, and politicians need to be seen by voters as doing everything possible to hold them down. Even optimistic forecasts currently have the one-way toll, now $2, nearing $7 by 2020 and $11 by 2030.

The airports authority board believes it’s able to do the right thing for the long term precisely because its members are appointed and don’t have to worry about elections. In the real world, though, the politicians ultimately control how public money is spent. The airports authority should gracefully accept that reality rather than risk a prolonged showdown that could kill a valuable project altogether.

I discuss local issues at 8:51 a.m. Friday on WAMU (88.5 FM).