By Harriet McLeod

CHARLESTON, South Carolina (Reuters) - South Carolina's attorney general sued President Barack Obama's administration on Tuesday over the federal government's rejection of the state's new voter identification law, arguing it would not disenfranchise any potential voters.

The Obama administration in December blocked South Carolina's law, signed by Republican Governor Nikki Haley in May, because of concerns it would hurt the ability of members of minority groups to cast ballots.

The law requires voters to show either a driver's license, passport or military identification along with a voter registration card at the polls. But a provision also allows them to vote without a photo ID if they sign an affidavit.

"Nothing in this law prevents anyone from voting if they cannot immediately show a valid photo identification," South Carolina Attorney General Alan Wilson said in a statement.

"The Department of Justice has denied citizens in South Carolina protection of a law that the U.S. Supreme Court upheld in Indiana, and the DOJ itself pre-cleared for Georgia," he said.

South Carolina is one of six Republican-led states that tightened their laws last year to require a photo ID. Two other Republican-led states have similar laws in place, while 23 more states require voters to produce some form of identification.

Under the South Carolina law, which supporters say would help prevent fraud, anyone who wants to vote but does not have a photo ID must obtain a new voter registration card that includes a photo. A birth certificate can be used to prove identity.

But the laws have often drawn objections from Democrats, who say they suppress the votes of people more likely to vote Democratic, such as African Americans, the elderly and the young.

The Justice Department said South Carolina's requirement could impede the voting rights of tens of thousands of people, noting that just over a third of the state's registered minority voters did not have a driver's license.

South Carolina is also one of several states that must have clearance from the federal government before changing voting laws because of its past record of using mechanisms such as literacy tests to suppress the black vote.

Wilson filed the lawsuit against the United States and U.S. Attorney General Eric Holder in the U.S. District Court for the District of Columbia.

"Like the Indiana law, South Carolina's photo identification law only places upon the voter an affirmative responsibility to obtain an approved photo identification card and to bring it to the polls," the suit said.

The photo ID requirements are a "temporary inconvenience no greater than the inconvenience inherent in voting itself," according to the complaint. A section of the law lets those who have no photo ID vote after signing an affidavit, Wilson said.

The Justice Department declined to comment on the suit.

The American Civil Liberties Union said on Tuesday it would intervene in the lawsuit on behalf of the federal government.

"The Department of Justice followed the letter and the spirit of the law when it rejected South Carolina's discriminatory voter ID law," Nancy Abudu, senior staff attorney with the ACLU's Voting Rights Project, said in a statement.

"Instead of fighting for this law in court, South Carolina and other states should focus on expanding the right to vote."

(Additional reporting by Jeremy Pelofsky; Editing by Colleen Jenkins and Cynthia Johnston)