WASHINGTON (Reuters) - The Supreme Court on Monday upheld a tough state law requiring voters to show photo identification, a decision critics say could keep some blacks, poor people and other traditional Democratic supporters from voting in the November election.

A woman leaves a voting booth for the Pennsylvania primaries at the Blue Mountain Fish & Game building in Danielsville, Pennsylvania, April 22, 2008. REUTERS/Shannon Stapleton

Resolving a partisan political battle, the country’s high court voted 6-3 to reject a legal challenge by Democrats that Indiana’s toughest-in-the-nation voter identification law would deter minorities, the elderly and others from casting ballots.

The main opinion agreed with Republican supporters that the law was necessary to prevent voter fraud and safeguard public confidence in the integrity of elections. The Bush administration supported the law.

The court handed down the ruling just eight days before the crucial Indiana presidential primary election featuring Democratic candidates Barack Obama and Hillary Clinton. If elected in November, Obama would be the first black U.S. president, while Clinton would be the first female U.S. president.

“The effect of the loss ... will begin to be felt next week when Indiana holds its presidential primary using the voter ID law the court has just upheld,” said Nathaniel Persily, an election law expert at Columbia University in New York.

The decision could have broad national significance because more than 20 states have adopted voter identification laws and other states are considering similar legislation.

The law requires a government-issued photo ID such as a driver’s license to vote in federal, state and local elections.

Indiana Secretary of State Todd Rokita, a Republican, said the timing of the ruling was good because it was the first time since 1968 that Indiana’s presidential primary had mattered and voter registrations had surged this year.

In seven elections since Indiana put the law into place, the requirement “hasn’t been an issue,” based on complaints to his office, Rokita said.

Reaction to the ruling split along political lines.

“This decision not only confirms the validity of photo ID laws but it completely vindicates the Bush Justice Department” when it approved a similar Georgia law, said former department official Hans von Spakovsky.

Democrats sharply criticized the ruling.

DENIES A FUNDAMENTAL RIGHT

“Denying a fundamental right -- the right to vote -- because a person is indigent, lacks a birth certificate or has no access to a vehicle goes against America’s better values,” Sen. Patrick Leahy of Vermont said.

Angela Ciccolo of the NAACP civil rights group said the law would have its greatest impact on voters who are poor, elderly, belong to racial minorities or have disabilities.

The lead opinion, written by Justice John Paul Stevens and joined by Chief Justice John Roberts and Justice Anthony Kennedy, held the evidence in the record did not support an attack now on the law’s validity.

Three other court members -- conservative Justices Antonin Scalia, Clarence Thomas and Samuel Alito, concurred in the judgment and issued a separate opinion that the law should be upheld because its overall burden was minimal and justified.

Stevens wrote that states had a “valid interest in protecting the integrity and reliability of the electoral process.” He said voter fraud “could affect the outcome of a close election.”

He said the law may place a small burden on a limited number of people -- the elderly born out-of-state who may have difficulty in getting the required documents, the homeless or people with a religious objection to being photographed.

Stevens said politics may have been a factor in adopting the law but that alone did not make it unconstitutional. His opinion left open the possibility of future legal challenges by specific voters.

Justices David Souter, Ruth Bader Ginsburg and Stephen Breyer dissented. Souter said the law threatened to impose major burdens on the voting rights of tens of thousands of Indiana residents, especially the poor and the elderly.