(Reuters) - A judge on Tuesday blocked Pennsylvania from requiring voters to show identification in November's U.S. election, a decision that could influence turnout in a top electoral prize in the presidential race.

Commonwealth Court Judge Robert Simpson issued a partial preliminary injunction that halts the requirement that people show either a state driver's license, government employee ID or a state non-driver ID card in order to vote on November 6.

The ruling comes exactly five weeks before the presidential election pitting President Barack Obama, a Democrat, against Republican contender Mitt Romney.

Simpson, on orders from the state's highest court to revisit his August ruling upholding the law, indicated the law could be implemented for future elections. He set a hearing for December 13 to schedule further proceedings in the case.

"This is a victory for the petitioners and people who will be able to vote on Election Day," said Marian Schneider, one of the attorneys for the groups challenging the law.

National attention has been focused on the court fight over the law requiring voters to show a photo ID. The Republican-led Pennsylvania legislature passed it in March without a single Democratic vote.

Supporters say it is aimed at ensuring only those legally eligible to vote cast ballots. Critics say it is designed to keep minority voters, who typically vote Democratic, away from the polls. Similar laws have generated controversy in other states.

The state of Pennsylvania has acknowledged that there has never been a case of in-person voter fraud, according to court testimony.

Simpson upheld the law in a ruling issued in mid-August. Last month, following an appeal of that decision, the Pennsylvania Supreme Court ordered him to re-hear arguments about whether the administration of Governor Tom Corbett was doing enough to ensure voters had "liberal access" to obtain picture ID cards needed to vote in November.

Groups such as the American Civil Liberties Union, League of Women Voters, Latino Justice, and SeniorLAW Center have argued that Pennsylvania's voter ID requirements make it impractical or nearly impossible for senior citizens, minorities and the poor to get the special voting card.

Simpson heard testimony last week from a dozen people who recalled the hurdles they had to overcome to get state-issued ID, including hourslong waits, multiple trips and misinformation. One of the witnesses, who included a person who walked with a cane and another in a wheelchair, described her experience as maddening and said she nearly gave up after several days' quest for the card.

Pennsylvania is one of the top prizes in the election, bringing the winner there 20 votes in the Electoral College, tying it with Illinois for fifth in the ranks of electors by state. Only California, Texas, New York and Florida bring more.

To win the White House, either Obama or Romney must capture at least 270 of the Electoral College's 538 available votes. A CNN poll released last week showed Obama with a 9 percentage point margin over Romney among likely voters in the state, leading 49 percent to 40 percent.

A raft of recently enacted voter ID laws are being challenged, and several have suffered setbacks in court this year.

Earlier this year, two judges in Wisconsin found that state's voter ID law violated the state's constitution, and last week the Wisconsin Supreme Court denied a fast-track appeal. Wisconsin Attorney General J.B. Van Hollen conceded the law was unlikely to go into effect before the election.

In August, a federal three-judge panel blocked a Texas law requiring voters to show identification. The U.S. Department of Justice had opposed the law, arguing it violated the Voting Rights Act of 1965, which outlaws voting procedures that discriminate against minorities.

The Department of Justice is also contesting South Carolina's voter ID law in federal court. Last week, a lawyer for South Carolina argued the law would not have a discriminatory effect and urged a panel of judges to let the law go into effect. But he did not insist a ruling come in time for the November 6 election.
(Writing by Barbara Goldberg and Dan Burns; Editing by Doina Chiacu and Jackie Frank)