Maryland’s attorney general asked an appellate court Friday to require a federal judge to decide a lawsuit blocking construction of the state’s planned Purple Line, saying court delays have “brought this project to the brink of cancellation.”

The petition for a “writ of mandamus” asks the U.S. Court of Appeals for the District of Columbia Circuit to require that U.S. District Judge Richard J. Leon rule on a government motion to dismiss the 2014 lawsuit filed by Purple Line opponents.

If there is no ruling by June 1, the state won’t have enough money to continue pre-construction work, according to the petition filed by lawyers for Attorney General Brian E. Frosh (D). At that point, the petition says, the state “likely” would direct contractors to stop design and engineering work on the light-rail project.

Suspending that work, the filing says, would add significant costs and could result in the 16-mile project being canceled.

“The fate of the Purple Line hangs in the balance,” the attorney general’s office wrote. “. . . That fate should be determined by policy makers responsible for the project and accountable to the public — or, if by a court, on the merits of the claim — rather than as a side-effect of inaction by the district court.”

A writ of mandamus requires a lower-court judge or government official to fulfill his or her official duties. The petition noted that such an action is an “extraordinary remedy” that courts don’t “lightly grant” but said Leon’s handling of the case had created an “extraordinary circumstance.”

Maryland officials have said waiting for Leon’s ruling has added $13 million every month to the line’s construction costs and could jeopardize a $5.6 billion public-private partnership to build and operate the line over 36 years. Canceling the project, state officials said, could cost the state more than $800 million in lost planning investments and contract termination costs.

Maryland officials need Leon to reinstate the project’s environmental approval before they can try to secure $900 million in federal construction funding. Leon revoked that approval in August after agreeing with the lawsuit’s plaintiffs that state and federal transit agencies hadn’t sufficiently considered the impact of Metro’s declining ridership on the future Purple Line’s ridership.

The plaintiffs — two Chevy Chase residents and the advocacy group Friends of the Capital Crescent Trail — say the Purple Line’s ridership forecasts are flawed because they didn’t account for Metro’s recent safety problems and declining ridership. The Purple Line between Montgomery and Prince George’s counties would be operated separately from Metro, but Metro riders are expected to account for about 27 percent of the light-rail line’s passengers.

In revoking the project’s environmental approval, Leon wrote that state and federal transit agencies had shown a “seemingly cavalier attitude” in initially dismissing any potential Metro impacts.

Federal transit officials said in December that further analysis had shown that Metro would have no significant impact on the Purple Line. But the plaintiffs have said Metro’s potential impacts are just one reason the light-rail line should be stopped because of its cost and environmental impacts.

In addition to questions about the ridership forecast, the state’s filing says Leon has yet to rule on 23 other issues in the case.