American Crossroads, the massive political action committee that helped propel Republicans into the House majority last fall, is planning to spend $120 million on a 2012 election cycle it is casting as a “David and Goliath” struggle between well-funded Democrats and underfunded Republicans.

The group’s chairman, Mike Duncan, told reporters Friday morning that 2012 would be the most expensive campaign cycle in history. He said that the so-called “super PAC” would go after President Obama early and often, perhaps attacking the incumbent on television before Republicans have settled on their nominee.

“We’re going to have $2 billion spent in the suspension of reality,” Duncan said, suggesting that Obama’s reelection campaign would raise $1 billion while the president’s allies on the left would spend hundreds of millions more.

Duncan said the campaign would be a “David and Goliath” struggle, adding that, although his group is budgeting $120 million for its efforts in the presidential race as well as congressional contests, “we will probably be outspent.”

At a breakfast roundtable sponsored by the Christian Science Monitor, Duncan and Steven Law, the group’s president and chief executive, said American Crossroads and its sister organization, Crossroads GPS, would not get involved in the Republican presidential nominating contest. “We just will not do that,” Duncan said.

And both men sought to separate their efforts from those of Restore Our Future PAC, a new super PAC founded by several former top aides to Mitt Romney that could be used to help the former Massachusetts governor in the GOP primaries. One of the new group’s founders, Carl Forti, who served as political director for Romney’s 2008 presidential campaign, is American Crossroads’s political director.

Asked about Forti working for both organizations, Duncan said: “Carl is a contract employee with American Crossroads ... he has other clients.” He added that, “Clearly, none of us are going to be involved personally with presidential campaigns.”

Law said: “We’re not concerned about it. Our mission is pretty clear. It’s very focused on putting attention and spotlight on President Obama’s record, his policies, and that’s not a very hard mission to stray from.”

Duncan said the emergence of super PACs like his is a natural outgrowth of what he called restrictions on giving to national political parties by campaign finance law.

“There’s not too much money in politics,” said Duncan, a former chairman of the Republican National Committee. “I firmly believe there is a role for various organizations. ... We spent more money on Halloween candies and costumes than we did in the election last year.”

American Crossroads plans to spend $120 million this year to help Republicans win the White House, defend their House majority and take back the Senate. Duncan said the group is eyeing nine or 10 Senate races, including helping defend Sen. Scott Brown (R) in Massachusetts.

“We think this is going to be a very lively and in some ways volatile election and we feel good about it,” Law said, adding: “I’m not sure that either side will have the wind at it’s back the way that we did last fall, so we’re just going to have to work hard and work smart.”