By Sharon Bernstein

(Reuters) - Wisconsin voters who do not have photo identification will be able to vote in November's presidential election, a judge ruled on Tuesday, the latest development in a long fight over a state law Democrats say is aimed at keeping minorities from the polls.

The ruling by U.S. District Court Judge Lynn Adelman temporarily eases the impact of a 2011 Wisconsin law requiring voters to show photo identification before being allowed to cast a ballot.

"Although most voters in Wisconsin either possess qualifying ID or can easily obtain one, a safety net is needed for those voters who cannot obtain qualifying ID with reasonable effort," Adelman said in his order.

Wisconsin is one of several Republican-led states that have passed such laws in recent years amid fear of fraudulent voting by illegal immigrants and others. The nine states with the strictest laws - insisting on state-issued photo identification for voters - include Texas, Virginia, Indiana and Georgia.

Republicans say voter ID laws are needed to prevent voter fraud. But Democrats say the laws are really intended to make it more difficult for poor African-Americans and Latinos - who skew Democratic in their politics - to vote.

Under Adelman's temporary injunction, people without ID can vote if they sign an affidavit at the polls declaring that they could not reasonably obtain photo identification and explaining why.

Allowable reasons include lack of a birth certificate or other documents required to obtain a photo ID, lack of transportation, disability and a tight work schedule.

Wisconsin Attorney General Brad Schimel, who had opposed allowing affidavits, could not immediately be reached for comment.

The ruling stemmed from a lawsuit filed against the state in 2011 by the American Civil Liberties Union and others on behalf of voters who said they were disenfranchised.

An earlier ruling by Adelman on the same lawsuit would have overturned the voter ID law entirely, but that was overruled by a federal appeals court, and last year the U.S. Supreme Court let the appeals ruling stand.

The case is now back with Adelman, who must decide whether to require the state to make the affidavit system permanent.

Richard Hasen, a law and political science professor at the University of California, Irvine, said that if the temporary injunction becomes permanent, it would soften Wisconsin's law.

"If it stands, it potentially blows open a big hole in the law," he said.

(Reporting by Sharon Bernstein in Sacramento, California; Editing by Jonathan Oatis)