Romney said he wasn't afraid to take on the tough issues.
"We're going to have to recognize that Social Security and Medicare are unsustainable, not for the current group of retirees, but for coming generations," Romney told the 2012 Conservative Political Action Conference. "And we can't afford to avoid these entitlement challenges any longer."
Romney said: "We are going to slowly and gradually raise the retirement age for Social Security" from the current 66 for full benefits. "And we'll slow the growth rate in benefits for higher-income retirees."
As for Medicare, "tomorrow's seniors should have the freedom to choose between Medicare and a range of private plans," Romney said to applause. "And if these future seniors want a more expensive plan, then they will have to pay the additional cost."
Romney also said he would balance the federal budget without cutting defense expenditures or raising taxes, and touted what he said was his conservative record as governor of Massachusetts.
Earlier at the conference, Santorum said the Tea Party is the heart of the Republican Party.
"We should recognize, as conservatives and Tea Party folks, that we are not just wings of the Republican Party," Santorum said. "We are the Republican Party."
Santorum took an oblique shot at Romney, the on-again off-again front-runner for the nomination, who is being touted as the most electable GOP candidate.
"The lesson we've learned is that we will no longer abandon and apologize for the policies and principles that made this country great [in exchange] for a hollow victory in November," Santorum said.
Santorum said he has put forward a plan "that says we are going to cut $5 trillion in five years, balance the budget in five years and in every year we will spend less money than the year before, year after year until ... the budget is balanced."
Romney and Santorum, a former senator from Pennsylvania, were followed at the conference by Gingrich, former speaker of the U.S. House.
Gingrich said he was in favor of giving "personal Social Security accounts for young Americans" and called for an audit of the Federal Reserve.
He said he would push for "maximum production" of domestic energy, and "if we get to maximum production our goal should be to get back to $2 a gallon gasoline. ... [President] Obama has been an anti-energy president and every American pays the price when he goes to the gas station."
After an early spurt, Gingrich's campaign has been sputtering. Once seen as the inevitable nominee, Romney has slumped since Santorum won nominating contests in Colorado, Minnesota and Missouri earlier in the week.
Conservative commentator Ann Coulter also spoke to the gathering and said she had a hard time figuring out why Romney has had a difficult time catching on in the Republican primaries -- finally deciding that he was like a "Ken Doll."
But Coulter said the country was "tired of hip" and was ready for a square president.