PURPLE LINE MAP (THE WASHINGTON POST/THE WASHINGTON POST)

The Federal Transit Administration has asked a federal judge to reconsider his order potentially delaying construction of the light-rail Purple Line in the Maryland suburbs.

U.S. District Judge Richard J. Leon of Washington on Aug. 3 ordered that the Maryland Transit Administration’s “record of decision” on the Purple Line — the federal stamp of approval on the project’s environmental analysis — be set aside until the state recalculates ridership projections to account for Metro’s deterioration and declining ridership.

Days after Leon’s ruling, Maryland officials canceled a public signing ceremony in which federal officials were to commit $900 million in grants toward the project’s $2-billion construction, the last major hurdle before construction.

In a filing late Tuesday, the U.S. Justice Department asked Leon to amend his ruling, saying he erred by requiring FTA to conduct a new impact study rather than letting the agency decide whether one was necessary, and by not allowing the record of decision to stand while a review is underway.

Artist’s rendering of the interior of planned Purple Line commuter trains in Maryland. (Purple Line Transit Partners) (Purple Line Transit Partners)

“The Court impermissibly substituted its judgment for that of FTA in making the ultimate finding that the information on WMATA Metrorail’s issues present a significant environmental impact,” lawyers for the FTA wrote.

The Maryland Transit Administration did not oppose the motion, a first step toward a potential appeal.

Federal and state lawyers have said a new ridership study could delay the project by six months and jeopardize a $5.6 billion public-private partnership that relies heavily on private construction financing.