MANCHESTER, N.H. — A Las Vegas billionaire has contributed $5 million to an independent group backing Newt Gingrich, bolstering the former House speaker’s efforts to revive his presidential campaign and drawing renewed attention to the role of such groups in the 2012 contest.

A person familiar with the development said Sheldon Adelson, a casino mogul and longtime donor to Republican candidates, made the contribution Friday to Winning Our Future, a super PAC run by Gingrich allies.

The person, who spoke on the condition of anonymity and was not authorized to discuss the matter publicly, said Adelson is expected to contribute as much or more to groups backing the Republican nominee, be it Gingrich or one of his rivals.

Rick Tyler, a former top Gingrich strategist and spokesman for Winning Our Future, declined comment on the donation, which was first reported by The Washington Post. Politico reported last month that Adelson was prepared to spend $20 million to help Gingrich.

A 2010 Supreme Court decision easing restrictions on corporate and individual spending laid the groundwork for these political action committees, or super PACs, which can raise and spend unlimited amounts of money to influence elections as long as they do not coordinate directly with a candidate’s campaign. The identities of those who contributed to super PACs in the second half of 2011 won’t be reported until the end of January.

Many donors’ names will never be known. Some super PACs have established nonprofit arms that are permitted to shield contributors’ identities as long as they spend no more than 50 percent of their money on electoral politics. Crossroads, the giant conservative outfit tied to former George W. Bush political adviser Karl Rove, operates both a super PAC and a nonprofit.

Crossroads and other Republican-leaning super PACs played a significant role in the 2010 midterm elections, helping deliver the House to the GOP and boost the number of Republicans in the Senate. The 2012 contest is the first to test the influence of such groups in presidential politics.

No candidate has seen his fortunes affected by the emergence of super PACs more than Gingrich.

Riding high in polls just a month ago, he became the target of a $3 million advertising barrage sponsored by Restore Our Future, a super PAC supporting Mitt Romney run by several of the former Massachusetts governor’s allies. The ads, which pounded Gingrich for his ties to federal housing giant Freddie Mac and his reversal on issues such as climate change, sent his political fortunes plunging in Iowa. Gingrich finished fourth in the state’s caucuses last week.

Romney and Gingrich tangled over the role of super PACs in a nationally televised debate Sunday. Romney said he had not seen Restore Our Future’s ads but defended their content.

“Governor, I wish you would calmly and directly state it is your former staff running the PAC,” Gingrich said to Romney, warning his own allies would be on the air soon.

Gingrich has pledged to carry on and is hoping to resuscitate his campaign in South Carolina, which holds its primary Jan. 21. With Romney heavily favored to win the New Hampshire primary Tuesday, his rivals are looking to slow his momentum when the contest moves to the South.

Several super PACs have already played a role in the Republican campaign. They include Make Us Great Again, a super PAC backing Texas Gov. Rick Perry; Our Destiny, supporting former Utah Gov. Jon Huntsman; and the Red White and Blue Fund, which helped revive Rick Santorum’s campaign in Iowa and is running ads in South Carolina.

Priorities USA Action, a super PAC backing President Barack Obama’s re-election campaign, has spent modestly during the Republican nominating contest and is expected to step up its role in the general election.

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