The battle over the biggest public transit project in Minnesota history shifted Wednesday to a federal courtroom in Minneapolis, where attorneys fought over whether it was too soon for a lawsuit from critics of the proposed route of the Southwest light rail.

U.S. District Judge John Tunheim said he’ll rule as soon as possible on a motion by attorneys for the Met Council and Federal Transit Administration to dismiss a suit by the Lakes and Parks Alliance of Minneapolis, which seeks to stall the $1.65 billion 16-mile line that would connect Eden Prairie to downtown Minneapolis.

Tunheim will hear arguments in March on a motion by the alliance to rule in its favor.

The alliance opposes a plan that includes building a tunnel through the Kenilworth corridor in Minneapolis, then routing the line on a bridge across a channel between Lake of the Isles and Cedar Lake. Freight rail tracks and a bike/pedestrian trail would remain at grade along the route.

The alliance contends that work on the project should not proceed until a supplementary environmental impact statement is complete on the effects of building the route through “an environmentally sensitive area.”

The group contends that deals cut with St. Louis Park and Minneapolis violate state law by ruling out options that should be part of any final decision.

“We’re saying, ‘Hit the pause button, hit the reset button, let’s start following the law,’ ” Lewis Remele, an alliance attorney, told Tunheim.

But Assistant U.S. Attorney Craig Baune said it was premature to sue since there’s been no final decision, and once the supplementary environmental impact statement is issued, there would be an opportunity for public comment.

“There is no threat that anything is being built anytime soon,” Baune said.

In a brief, the Met Council argued that the project is “not ripe for judicial review, and the state law on getting municipal consent provides no private right for legal action.” The Minneapolis City Council has signed off on the route.

One environmental impact statement was completed in 2012, and a supplementary one is being conducted to evaluate changes in the design.

The government entities argue that it is not an abuse of their discretion to make agreements with municipal governments while an environmental-impact statement is in process.

The alliance countered in its brief that doing an environmental assessment after alternate routes are eliminated through agreements limits “the reasonable alternatives for the project” and can result in “irreparable injury.”