LIKE THE GREEK economy, the $6 billion project to build Metro’s Silver Line extension to Dulles airport and into Loudoun County has faced so many critical junctures that its recent history resembles the “Perils of Pauline.” Still, Dulles rail’s current cliffhanger, which may come to a climax Wednesday, may be the most decisive yet.

The immediate question is whether the Metropolitan Washington Airports Authority, which is building the Silver Line, will drop its stated preference for a union-friendly contract for the project’s second phase of construction. It should, because it’s the only way to maintain the project’s momentum — and because the contract is likely to turn out the same way anyway.

The debate over a project labor agreement ( PLA), which sets wages and working conditions in return for smooth labor relations and flexible work schedules, is no longer about the facts, unfortunately. If it were, a plausible case could be made in favor of a PLA; after all, Bechtel Corp, the general contractor for the first phase of Dulles rail, has managed quite well with just such an arrangement.

Rather, the debate has morphed into an ideologically charged litmus test for Republican lawmakers who control the purse strings in Richmond and Loudoun. Prodded by the construction lobby, and with little regard for the project itself, they have demonized PLAs as sweetheart deals for unions that violate the state’s anti-union right-to-work laws and add millions of dollars in unnecessary costs.

In fact, most major highway construction projects in Virginia operate with PLAs as a matter of course — though they are not required or favored by the state as a contractual condition. Any general contractor selected for the Silver Line’s second phase is likely to opt for a PLA as well — with no objection from the state. That’s the irony of this dispute: The airports authority was picking a largely gratuitous fight.

At this point, it doesn’t matter. Dulles airport is in Virginia; the Silver Line is being built in Virginia; anti-union Republicans control the governor’s mansion and Virginia legislature; and political discourse is too polarized for rational argument. If the airports authority wants Virginia’s help, it has to accede to Virginia’s wishes — which include dropping any explicit, up-front incentive that favors a PLA.

And the Silver Line does need Virginia’s help. Richmond has given just $274 million to the project, less than 5 percent of its total cost. It has pledged a further $150 million — still paltry, considering the project’s vast potential benefit to Virginia’s economy — but only if the airports authority drops its PLA tilt.

Just as critically, the all-Republican board of supervisors in Loudoun says it will withdraw from the Silver Line deal — and sacrifice its two planned Metro stations in the bargain — unless the PLA preference disappears. That would force a legal, financial and environmental restructuring of the second phase of construction that could delay the project by 18 months or more and inflate costs.

The real threat to the Silver Line at this point is not a PLA. It’s ego, pride, politics and ideology. Conservative Republicans in Richmond have dug in against a quasi-public authority it perceives as pro-union. Both sides need to take a deep breath. On Monday, Gov. Robert F. McDonnell (R) took a step in that direction by promising to unlock the state’s $150 million, with no other strings attached, if the airports authority drops its PLA preference. Good for him.