A panel of three federal judges struck down the Massachusetts Legislature’s 2001 redistricting plan Tuesday on the grounds that it violates black voters’ rights “to participate in the political process and to elect representatives of their choice.” The court gave lawmakers six weeks to redraw district lines fairly.

The proposed redistricting plan, which the House Redistricting Committee drafted after the 2000 census, did not create a number of “majority-minority” districts – districts comprised of more than 50 percent minority voters – proportional to the actual minority population in Boston, the court ruled. Several groups, including the Black Political Task Force and Boston VOTE, challenged the Legislature’s redistricting plan and argued their case in front of the appeals court in December.

“The enacted plan fails to provide African-American voters with a proportional number of majority black districts,” wrote Bruce Selya, a judge for the U.S. First Circuit Court of Appeals, in the panel’s unanimous decision. “The other side of the coin is that the enacted plan provides white voters with a number of majority white districts that exceeds proportionality.”

The disparity violates the federal Voting Rights Act, the court ruled. Legislators claimed their plan provided nine majority-minority districts of the 17 legislative districts in Suffolk County, but the court ruled that only one or three districts were actually majority-minority, depending on how the data was calculated.

“We deem it encouraging that African-American voters in Boston have enjoyed a modicum of success in electing candidates of their choice outside of majority black districts,” Selya wrote. “At the same time, however, we find it telling that the enacted plan provides for only one majority black district.”

“In our judgment, their creative mathematics do not add up,” the court said.

The court also found that incumbents drew the new districts to protect their seats.

“The committee made African-American incumbents less vulnerable by adding black voters to their districts and made white incumbents less vulnerable by keeping their districts as ‘white’ as possible,” the court ruled. “This course of conduct sacrificed racial fairness to the voters on the altar of incumbency protection.”

Furthermore, the court said committee members consciously packed the new districts.

“To make a bad situation worse, the House leadership knew what it was doing. [House] Speaker [Thomas] Finneran admitted that the sixth Suffolk was a ‘safe’ majority black district before the six new precincts were transferred to it.”

The ruling also said Rep. Thomas Petrolati (D-Ludlow), the chairman of the redistricting committee, knew that the sixth Suffolk district had an “exceedingly high concentration of African-American voters.”

But Petrolati defended the plan in a statement Tuesday, saying the committee took input from the public in five public hearings and “sought and listened to representatives of diverse communities.”

“It is my opinion that we met the needs of these communities,” Petrolati said.

“While I respectfully disagree with the court’s decision, I will work with the members of the committee with all due diligence to meet the requirements of the court within the time the court has set,” he said.

Boston VOTE Policy Director George Pillsbury said the ruling was a victory for equal rights.

“The plaintiffs are overwhelmed and really excited about the tremendous victory for black and Latino voters in Boston,” he said. “It really also says the Voting Rights Act still means something … 40 years later.”

But Pillsbury cautioned that Tuesday’s ruling was not the end of the case because the new district lines still have to be drawn and approved.

“It’s an immediate victory, but the victory remains to be had,” he said.

The redistricting committee has six weeks to draft a new plan, get input from the plaintiffs and submit it to the court for approval. If the plan is not approved or not submitted on time, the court will draw the new districts.