In a key twist to the 2012 election, US President Barack Obama has reversed course and will encourage rich Democratic donors to back a fund that can raise unlimited millions for his reelection bid.

Obama's campaign manager Jim Messina said Obama would allow cabinet members and senior advisors to address big money events, reasoning that Democrats could not be "unilaterally disarmed" in the face of a Republican cash landslide.

Political committees known as super PACS have mushroomed since a 2010 Supreme Court ruling that gutted campaign finance laws and let corporations and individuals give unlimited sums to outside groups backing candidates.

A torrent of special interest money has poured into the Republican White House nominating race since the ruling, and Obama would have stood at a significant disadvantage if he did not conquer his qualms and back a super PAC.

The groups have unleashed a barrage of negative, damaging advertising and are certain to target Obama as he seeks a second term in November.

In one example of the new power of the super PACS, a group loyal to Republican frontrunner Mitt Romney spent millions castigating his foe Newt Gingrich before January's Iowa caucuses.

Gingrich meanwhile has been kept in the race largely by a super Pac financed by a friend who is a casino tycoon.

"Our campaign has to face the reality of the law as it currently stands," said Messina in a message to Obama supporters, pointing out that Republican super PACS had spent $40 million in the last two months alone.

"With so much at stake, we can't allow for two sets of rules in this election, whereby the Republican nominee is the beneficiary of unlimited spending and Democrats unilaterally disarm."

Democratic sources had suggested that Obama believes the role of super PACS had been a corrosive influence on the already money-soaked world of US politics and that he had been reluctant to get involved.

But Messina said that the campaign would support the Priorities USA Action super PAC that was set up to support Obama but has so far failed to raise campaign cash in the huge quantities piled up byRepublican candidates.

Though White House aides and officials will attend super PAC events, Obama, First Lady Michelle Obama and Vice President Joe Biden will steer clear of such events and concentrate on raising cash for Obama's official campaign.

The decision will likely expose Obama to claims of hypocrisy, however, as he famously criticized Supreme Court members for "opening the floodgates" to special interest cash during his State of the Union speech in 2010.

It also recalls an earlier reversal by Obama, who had railed at the influence of money in politics, but during his 2008 campaign became the first major candidate since the Watergate scandal to refuse public financing.

The decision allowed then-senator Obama to torch candidate spending limits and raise a record $745 million dollars for his presidential campaign.

Messina said, however, that despite boosting Priorities USA Action, the Obama campaign continued to believe that November's election would be won with a grassroots political ground game underpinned by small, individual donors.

In one campaign fundraising drive this month, the Obama reelection effort has been asking donors for as little as $3 towards his campaign -- and has so far raised nearly $2.6 million.

The Obama campaign believes that pooling the cash of hundreds of thousands of people giving small amounts is the most effective way to organize, as it builds grass roots supports and donor banks that can be repeatedly tapped.

Messina said the campaign hoped to "ensure that the decisive factor in this election won't be an unprecedented flood of special-interest spending, and (that) the outcome will be in the hands of ordinary Americans."

Obama had raised $125 million for his presidential campaign up to the end of December, compared to Romney who had banked $56 million at the same time as he is running for his party's nomination, according to campaign fundraising tracking website

But Republican-affiliated super PACS, including American Crossroads, set up by George W. Bush's former political guru Karl Rove, have far out-raised liberal and Democratic groups.