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  (Photo: REUTERS/Jonathan Ernst)
  Drawings of Republican U.S. presidential candidates Newt Gingrich, Mitt Romney, Rick Santorum and Ron Paul are displayed at a booth at the American Conservative Union's annual Conservative Political Action Conference (CPAC) in Washington, February 9, 2012.

Republican presidential front-runner Mitt Romney sought to defend his conservative credentials at the Conservative Political Action Conference Friday but received a milder response than his opponent Newt Gingrich, who vowed to repeal all of Obama's landmark bills if elected.

"I was a severely conservative Republican governor," former Mass. Gov. Romney told the crowd at CPAC 2012 in Washington, D.C. Friday, as he sought to prove his credentials.

Romney's main rival is former Penn. senator Rick Santorum, who swept three caucuses and primaries Tuesday posing a threat to his front-runner status. But he may also need to watch former House Speaker Gingrich, whose promise to repudiate President Barack Obama's legacy stole the show at the conservative conference.

"[B]y Jan. 20, when I am sworn in, it will have repealed Obamacare," Gingrich said, noting that he would ask Congress to begin repealing Obama's bills beginning Jan. 3, after the Christmas recess. "It will have repealed [the Dodd/Frank financial reform bill]. It will have repealed [the] Sarbanes-Oxley [Act]...That's a reasonable start."

While Romney was applauded when he spoke about his support of traditional marriage and abstinence education in Massachusetts, the cheering was not as loud as for Gingrich. "By the time President Obama lands in Chicago we will have repudiated at least 40 percent of his government on the opening day," said Gingrich, who won the South Carolina primary last month.

Romney, on the other hand, flaunted his family life and business experience. "My path to conservatism came from my family, my faith, and my life's work," he said. "My 42-year marriage to my wife, Ann, the life we've built with our five sons, and the faith that sustains us – these conservative constants have shaped my life."

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He said he started new businesses and turned around broken ones, and "I am not ashamed to say that I was very successful at it." He added that he knows conservatism "because I have lived conservatism." However, he excluded his health care reform, which critics say influenced the federal health care law, from his speech.

Gingrich, who converted to Catholicism in 2009, remained focused on Obama. He lambasted his administration and the courts for "waging war on religion."

"This is why we need a movement that's bigger than just beating Obama," he said.

He also criticized the Republican establishment, saying it seeks to "manage the decay" rather than "change the trajectory" as "changing the trajectory requires real fights and a real willingness to roll up sleeves and actually take on the left."

"They don't have the toughness, they don't have the commitment, and they don't have the philosophy necessary to grow a majority in this country," he said.