Washington ? The Supreme Court gave politicians new legal license Wednesday to redraw election districts aggressively to benefit the party in power, as it upheld the mid-decade redistricting plan engineered by former House Majority Leader Tom DeLay and Texas Republicans.

By clever line-drawing, Delay and the Texas legislature – with both houses newly under GOP control in 2003 – remade its delegation in Congress, helping turn a 17-15 Democratic majority into a 21-11 Republican majority in 2004.

The bold move signaled an escalation in partisan warfare. Before, the redrawing of the electoral districts was a once-a-decade battle that followed the release of new census numbers.

Legal experts and political strategists said Wednesday’s ruling will encourage Republicans in other GOP-dominated states to redraw their districts to give themselves a bigger majority.

It is not clear that Democrats will be able to do the same. In the ruling Wednesday, the court stressed that the Voting Rights Act generally forbids splitting up blocs of minority voters. That makes it harder to create more Democratic districts.

Mary G. Wilson, president of the League of Women Voters, called the decision “extremely disappointing,” saying it will encourage politicians to become serial mapmakers. “We now can expect an even more vicious battle between the political parties as they redraw district lines every two years for partisan gain,” she said.

On Wednesday, a five-member Supreme Court majority said that DeLay’s plan, even if it were drawn for a purely partisan purpose, did not violate the Constitution and its guarantee of equal protection under the law. But the court did find one district to be illegally drawn because it diluted Hispanic voting power. The overall ruling applies to other electoral districts as well, including those for state legislatures.

Electoral districts are usually drawn by politicians in state capitals, the justices noted, and it is hard to say when such a politically drawn plan becomes too partisan.

Justice Anthony M. Kennedy, speaking for the court, cited two other reasons for upholding the Texas plan.

First, he said, the task of redistricting belongs to elected legislators. In 2001, a panel of federal judges redrew the Texas districts because the state legislature – then divided between a Republican Senate and a Democratic House – could not agree on a plan. So the plan pressed by Delay in 2003 was the first to win the approval of the state’s elected legislators.

Second, he said, it is not clear that the GOP-friendly plan drawn by DeLay was less fair than the Democratic-friendly plan it replaced.

Prior to 2003, Democratic leaders had used their power in Austin to preserve a Democratic majority in the state’s congressional delegation, even as most Texans voted for Republicans. Four years ago, 59 percent of Texans voted Republican and 41 percent Democratic in statewide tallies, yet more Democrats than Republicans won election to the House of Representatives.

By this measure, DeLay’s plan “can be seen as fairer” than the one it replaced, Kennedy said.