A three-judge panel hearing a challenge to Maryland’s plan for once-in-a-decade redistricting expressed disbelief Tuesday when an attorney for the state said there was no evidence that Democrats had gerrymandered the state’s congressional map.

But the judges expressed even more skepticism that members of a grass-roots civil rights group and their Republican-funded legal team had proved that Maryland lawmakers intentionally diluted the voting power of minorities.

The odd coalition of plaintiffs — mostly black community organizers from Prince George’s County and the conservative-funded Legacy Foundation — contended that the surging minority population in Washington’s Maryland suburbs was carved up to help elect or reelect white Democrats.

The plaintiffs asked the judges — Paul V. Niemeyer of the U.S. Court of Appeals for the 4th Circuit and Alexander Williams Jr. and Roger W. Titus, both of the U.S. District Court for Maryland — to toss out the map and require a new one consolidating blacks in a third majority-minority district.

“It seems . . . you want us to make a political decision,” Niemeyer told the plaintiff’s lead attorney near the end of a three-hour hearing at the federal courthouse in Greenbelt.

But the judges also appeared to be searching for a rationale to improve the map, suggesting at several turns that they viewed the plan proposed by Gov. Martin O’Malley (D) and approved by the state’s Democratic-controlled legislature as deeply flawed.

Niemeyer promised the panel would attempt to rule quickly so that Maryland’s scheduled April 3 primary elections could go forward if the map withstands legal scrutiny.