HARRISBURG, Pa. (AP) - Not long after the 2000 Census, the Republicans in the state Legislature used their muscle to redraw Pennsylvania's congressional map and essentially redistricted three Democratic House members out of a job.

On Wednesday, the U.S. Supreme Court will hear arguments on whether the GOP went too far, in a case that could alter the nation's political landscape by determining how big a role party politics can play in the drawing of voting districts.

A group of Democrats is asking the court to spell out rules limiting partisan gerrymandering, the practice of drawing districts to favor one party over another.

The Republicans are arguing that redistricting is inherently political and should be left to the politicians in the Legislature.

At issue is 1986 Supreme Court decision that suggested partisan gerrymandering could be unconstitutional if taken too far. However, the court did not specify what would constitute excessive gerrymandering.

If the high court backs away from that ruling, as the GOP is urging it to do, the Republicans could lock in their control of Congress for years to come, said Nathaniel Persily, a professor and redistricting expert at the University of Pennsylvania Law School in Philadelphia.

But if the justices endorse the greater judicial involvement the Democrats seek, the ruling would probably lead to legal challenges to the new congressional maps in at least a half-dozen other big states, he said.

"Once the court opens the door just a little, everyone is going to try to rush through," Persily said, summarizing the conventional wisdom this way: "If you have a chance of striking down a redistricting plan that hurts your party, you might as well make the claim, even if you think your chances of success are minimal."

The case is being closely watched by officials in Texas, where a bitter court fight over redistricting also involves Democratic charges of blatant GOP gerrymandering.

The case "really brings to the Supreme Court, for the first time in nearly 20 years now, the issue of partisan bias in its clearest and perhaps one of its more excessive forms," said Gerald Hebert, a Virginia lawyer for a group of Texas Democrats who filed a brief in support of the Pennsylvania plaintiffs.

States must redraw boundaries after every census to reflect population shifts.

Because of Pennsylvania's slower-than-average population growth, the state lost two of its 21 seats in Congress after the 2000 census.

The new 19-seat maps were approved with substantial Democratic support, but were engineered by the Republicans who control both houses of the Legislature, at a time powerful computer software makes it possible to trace voting patterns down to individual streets and houses.

Largely because of where the district boundaries were drawn, the GOP won 12 of the 19 seats in 2002, tightening their grip on the state's congressional delegation. Previously, the Republicans had 11 seats to the Democrats' 10.

The GOP acknowledges using the maps to enhance its election prospects in 2002, but insists it did nothing illegal.

"These days," said Jack Krill, the lawyer representing the state Senate president pro tem and the House speaker, both Republicans, "a gerrymander is merely a redistricting plan that somebody doesn't like."

Among other things, the new map corralled six Democratic incumbents into three districts. Two of them chose to retire rather than challenge their Democratic colleagues in the primary. In the third district, Rep. Frank Mascara was defeated by Rep. John Murtha.

In 2002, a panel of three federal judges largely upheld the new map, with minor changes.

The Democrats want the Supreme Court to build upon the 1986 decision, which involved state legislative redistricting in Indiana, and set standards for determining when gerrymandering violates the Constitution, just as the court did in outlawing racial discrimination in redistricting since the 1960s.