Maryland leaders and transit activists called on a federal judge Tuesday to issue a ruling allowing the Purple Line to be built in the Washington suburbs, saying a delay in a court case blocking the project is costing taxpayers money.

The light-rail plan to connect Montgomery and Prince George’s counties needs a favorable court ruling to get its federal environmental approval reinstated before it can secure $900 million in federal grants and begin major construction.

“Let me just say very politely, ‘Judge, your delay in making a decision is costing taxpayers money — every day, every hour,’ ” Montgomery County Executive Isiah Leggett (D) said at a rally in downtown Silver Spring.

Purple Line construction remains on hold as U.S. District Judge Richard J. Leon reconsiders his August decision to revoke the line’s environmental approval. The ruling, which favored the plaintiffs in a lawsuit filed by Purple Line opponents, made the project ineligible for federal funding. It came days before Maryland officials were scheduled to sign an agreement for nearly $1 billion in federal construction aid.

Prince George’s County Council member Dannielle M. Glaros (D-Riverdale Park) said her community is counting on the line to connect residents to jobs and rejuvenate aging inner-Beltway suburbs.

“Every day we wait, we cost taxpayers money, and we lose economic development opportunities along the line,” Glaros said.

Criticism about the amount of time Leon has taken to reconsider his decision was more muted Tuesday than Maryland Gov. Larry Hogan’s recent public allegation that the judge is biased. Hogan (R) told reporters, inaccurately, that Leon lives at a country club in the path of the 16-mile Purple Line alignment and that the judge’s wife was involved in an opposition group.

About 100 Purple Line supporters gathered on an outdoor patio of the new Silver Spring library — an area designed to be a future Purple Line station — amid the grinding noises of an apartment building under construction nearby. A sign behind the podium announced that construction on the rail station there would be “starting soon.”

“We are building here, and we did so in anticipation of the Purple Line being here,” Leggett said.

Maryland officials have said the state has spent more than $380 million on planning and designing the project and would lose hundreds of millions more in contract penalties if it is canceled. The Maryland Transit Administration (MTA) has signed a 36-year, $5.6 billion contract with a consortium of companies to help finance construction, build the line and then operate and maintain it.

If the court ruling favors the project, major construction could begin within a few weeks, state officials have said.

Purple Line supporters cheered as activists noted that Congress is expected to approve a federal spending bill that includes $125 million toward the Purple Line’s $2 billion construction.

However, that $125 million, as well as another $200 million previously designated for the project, is contingent upon Maryland officials signing a federal funding agreement before the fiscal year ends in September.

“Congress has made itself clear — we want the Purple Line built,” Rep. Jamie B. Raskin (D-Md.) said.

Purple Line supporters faced questions from the media about whether it was proper to demand that a federal judge issue a ruling on their timetable, rather than his own.

“It’s not wrong for us to ask the judge for a timely decision,” said Prince George’s County Executive Rushern L. Baker III (D). “All the information is in there. This is too important.”

Under the original schedule, Purple Line construction was to begin last October, with trains carrying passengers in spring 2022.

However, construction was delayed indefinitely after Leon ruled that the Purple Line’s federal environmental approval did not adequately consider what impact Metro’s declining ridership could have on the Purple Line’s ridership. The Purple Line would be operated by the state but would connect to four Metro stations.

The Purple Line’s projected ridership was part of the environmental study that analyzed the cost effectiveness of light-rail versus a bus line.

Opponents have argued that federal and state officials did not sufficiently consider Metro’s falling ridership when they chose light rail for a Purple Line over a rapid-bus line that would be less expensive and spare a wooded recreational trail.

The Federal Transit Administration (FTA) asked Leon to reconsider his August decision, and the Maryland attorney general had asked for a ruling by last Friday — a deadline that came and went. In December, the FTA told the judge that the Purple Line would have sufficiently strong ridership, even without passengers connecting to the Metro system.

Maryland transit officials recently said the project remains on schedule, even with the delays, because they can “resequence” the work.