By Colleen Jenkins

WINSTON-SALEM, N.C. (Reuters) - A U.S. federal court on Tuesday set a March 15 deadline for North Carolina state lawmakers to redraw legislative districts found to be racially "gerrymandered," and ordered a new round of elections by next November for the 28 seats at stake.

In August, the same special three-judge panel ruled that nine state Senate districts and 19 state House districts, as carved out in a plan adopted by the Republican-controlled legislature in 2011, were unconstitutional.

The panel had told North Carolina's legislature to start revamping its political maps immediately, but left the existing boundaries intact for the Nov. 8 state elections, because of time constraints.

"While special elections have costs, those costs pale in comparison to the injury caused by allowing citizens to continue to be represented by legislators elected pursuant to a racial gerrymander," the panel wrote in its seven-page order on Tuesday.

North Carolina has already appealed the August ruling to the U.S. Supreme Court, which has yet to act. Republicans also vowed to appeal Tuesday's ruling, handed down by two U.S. district judges and one circuit judge.

The ruling is a "politically motivated" abuse of judicial authority, said state Senator Bob Rucho and Representative David Lewis, the Republican chairmen of the House and Senate redistricting committees.

If upheld, the court order "is a gross overreach that blatantly disregards the constitutional guarantee for voters to duly elect their legislators to biennial terms," they said.

Last year, the Southern Coalition for Social Justice challenged North Carolina's latest political maps, saying legislative district lines were drawn in 2011 so as to dilute the state's black vote and give Republicans an advantage.

The three-judge panel that heard the case agreed, and Tuesday's order, essentially an extension of its August opinion, was hailed by the North Carolina Democratic Party.

A separate three-judge U.S. court panel ruled in a similar case a week ago that state assembly districts in Wisconsin, as redrawn by its Republican-led legislature, were unconstitutionally gerrymandered.

Tuesday's North Carolina ruling sets a deadline of March 15 for newly elected legislators to approve a redistricting plan that passes constitutional muster.

It also requires the state to hold special primary and general elections in the late summer and fall of 2017 to fill those 28 House and Senate seats.

Moreover, state lawmakers elected to any of the disputed General Assembly seats in 2016 will serve for just one year, instead of the normal two, the court ruled, a limit set for those elected next fall as well.

(Writing and additional reporting by Steve Gorman in Los Angeles; Editing by Clarence Fernandez)