By Terry Baynes 

Oct 12 (Reuters) - President Barack Obama's re-election campaign on Friday urged the U.S. Supreme Court to uphold lower court decisions allowing in-person early voting in the battleground state of Ohio in the three days before the Nov. 6 general election.

Ohio, critical to both Democrat Obama and Republican challenger Mitt Romney, began early in-person voting last Tuesday but planned to cut it off on Nov. 2, the Friday before the Nov. 6 election, except for members of the military.

The Obama campaign, the Democratic National Committee and the Ohio Democratic Party had sued Ohio officials to restore early voting right up to election day eve. Republicans opposed their efforts, saying a cutoff was needed to reduce voter fraud.

Last week, the 6th U.S. Circuit Court of Appeals upheld a U.S. District Court order that reinstated early voting in the final days before the election.

Ohio's top election official, Secretary of State Jon Husted, a Republican, asked the U.S. Supreme Court on Tuesday to overturn that decision. In a response filed on Friday evening, Obama's campaign asked the high court to let the 6th Circuit decision stand.

The Obama campaign's court document said Ohio "settled on a voting procedure unheard of in any other state" and that two courts had found it would "significantly burden tens of thousands of Ohio voters and likely violate" their constitutional rights.

It said the Republicans sought an emergency suspension of the appeal's court decision "but have utterly failed to carry their burden of showing that a stay is warranted."

The U.S. Supreme Court is expected to issue its ruling soon, with the election just more than three weeks away.

Early voting and extended voting hours are thought to benefit Democrats because lower-income people, who tend to vote Democratic, are more likely to work odd hours.

Husted called the 6th Circuit's decision an unprecedented intrusion by federal judges into state elections that was illegal and impractical.

The appeals court's decision did not require polls to be open on the final three days, leaving it up to the discretion of the state's 88 individual county election boards.

A coalition of 15 states, including Colorado, Wisconsin and Virginia, filed a supporting brief for Ohio on Friday, encouraging the court to block the 6th Circuit's ruling. They said Ohio had not placed a burden on citizens' ability to vote by eliminating the three early voting days.

The case is Husted et al v. Obama for America et al, U.S. Supreme Court, No. 12A338. 

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