ASHINGTON, June 27 — Taking up a highly charged issue of partisan politics, the Supreme Court agreed today to decide whether Pennsylvania's Democrats were victims of an unconstitutional partisan gerrymander at the hands of the Republican-controlled Legislature in Congressional redistricting after the 2000 census.

The case will be argued in the court's next term. It was one of five new appeals that the justices granted on a final cleanup day before the summer recess. In the absence of any retirement announcements in this final week, the prospect that any member of the court is planning to retire this year appears extremely remote, last-minute rumors to the contrary.

Pennsylvania, where registered Democrats outnumber Republicans by 3.7 million to 3.2 million, lost two seats in the House of Representatives as a result of the last census. The Legislature then drew new district lines with the goal of favoring Republicans to the greatest degree possible.

In two districts, pairs of Democratic incumbents were required to run against one another. Another Democratic incumbent was placed in a heavily Republican district. Counties were split and districts given highly irregular shapes in order to create Republican supermajorities.

As a result, the state's Congressional delegation went from 11 Republicans and 10 Democrats to 12 Republicans and 7 Democrats.

Three Democratic voters sued in federal court, claiming that the redistricting had deprived them of their right to equal protection. A 1986 Supreme Court decision in a partisan gerrymandering case from Indiana opened the door to this constitutional argument, but the decision provided few guidelines for its application and has been invoked reluctantly and inconsistently in the lower courts.

A special three-judge federal district court in Harrisburg dismissed the Democrats' case on the ground that they had not demonstrated sufficient injury, which the court defined as being "completely shut out of the political process." In their appeal, the Democrats are asking the justices to take a new look at the 1986 precedent, Davis v. Bandemer, and "clarify that extreme partisan gerrymandering is not only justifiable in theory but remediable in actual practice."

For their part, the Republican legislative leaders are asking the court instead to overturn the precedent and remove political gerrymanders from the jurisdiction of the federal courts. This was the position expressed in dissent in the 1986 case by Justice Sandra Day O'Connor and Chief Justice William H. Rehnquist, who was then an associate justice. Warren E. Burger, who was then chief justice, also dissented in Davis v. Bandemer.

The Pennsylvania legislative leaders told the justices in the case today that the fears the dissenters expressed in 1986 had come to pass as partisan battles were shifting from the political arena to the courts.

"To permit challenges to duly-enacted Congressional redistricting legislation on the basis of partisan gerrymandering delegitimizes the political process," the Republicans' brief said.

The case is "incredibly significant," said one election law expert, Richard Pildes of New York University Law School. He said gerrymanders of one kind or another have helped create district maps that have left the great majority of House seats uncompetitive.

Partisan gerrymander battles have erupted in Michigan and Florida. In Texas last month, House Democratic lawmakers fled to Oklahoma to deprive Republicans of a quorum for a redistricting plan, while in Colorado, Republicans succeeded last month in accomplishing a favorable and highly unusual second postcensus redistricting.

"We are losing the ability to put on meaningful elections," Professor Pildes said in an interview. "It's become a terrible problem in the system. It's become almost like the Middle East — both sides recognize that the situation isn't good, but they can't let go. There needs to be outside intervention."

He said the court's decision to hear the case, Vieth v. Jubelirer, No. 02-1580, might reflect the justices' recognition of a problem that requires their attention.

The Pennsylvania Democrats, represented by a Washington lawyer, Paul M. Smith, quoted judges and scholars who have recently called on the court to address partisan gerrymandering. Richard A. Posner, the federal appeals court judge in Chicago, argued in a recent book that "judicial insouciance" toward partisan gerrymanders and the creation of safe seats had undermined "electoral competition, the lifeblood of democracy."

In rejecting the Democrats' case, the district court in Pennsylvania said that in order to bring a successful challenge to a partisan gerrymander, plaintiffs must show that they have been not only outmaneuvered, but also cut out of the political process, to the extent of not being able to register, organize, campaign or raise money.

This was a good 24 hours for Mr. Smith, the Democrats' lawyer; he made the winning argument in the gay rights case the court decided on Thursday. By coincidence, Bowers v. Hardwick, the precedent the court overruled on Thursday, was decided on the same day in 1986 as Davis v. Bandemer, the gerrymander decision at the center of the new appeal.