Mitt Romney gave a detailed defense of his own conservative credentials Friday before a convention of right-wing activists, telling them that his life as a businessman and Massachusetts governor had been a series of battles for Republican ideals.

“I know conservatism, because I have lived conservatism,” Romney told a packed ballroom at the Conservative Political Action Conference, in a speech in which he underlined the point by saying “conservative” or “conservatism” 24 times. At some points, even those words weren’t strong enough: Romney called himself a “severely” conservative governor in Massachusetts.

“I have been on the front lines,” Romney said. “And expect to be on the front lines again.”

Romney’s speech came on a day when all three of the GOP’s leading contenders will take the stage at the Marriott Wardman Park in Northwest Washington. Former senator Rick Santorum (R-Pa.) spoke to a cheering, whistling crowd earlier in the day, and former House speaker Newt Gingrich (Ga.) will appear this afternoon.

As Romney spoke, the crowd rose to applaud at least six times. He said that his own experience in business and in state government had left him better prepared to tackle Washington problems than Santorum and Gingrich, both of whom are veterans of Capitol Hill.

“I happen to be the only candidate in this race, Republican or Democrat, who has never worked a day in Washington,” Romney said. Even four years in the Massachusetts statehouse had not changed him, he said: “I served in government, but I didn’t inhale. I’m still a business guy.”

Romney has spent the past few months trying to transform himself from a presumed front-runner into an actual front-runner for the GOP nomination. But he has lost four primary contests to Santorum and one to Gingrich, in part because conservative voters have deserted him.

The speech Friday was designed to change that: The CPAC conference is the country’s best-known gathering of conservatives, and Romney’s talk was scheduled between panels blasting President Obama’s health-care law and other Democratic ideas.

The people in this ballroom were at the core of Romney’s problem.

Romney’s talk went over several pieces of his agenda. He pledged to cut government spending, overhaul Medicare for future seniors and raise military budgets. He also promised to repeal the health-care law — a touchy subject for Romney, since he signed a state law in Massachusetts that works in similar ways.

Like many speakers at the conference, Romney said that, if Obama is reelected, the result would be a fundamental change in the values that make America great. That fear could turn out to be his strongest argument, if conservatives decide that Romney — whatever his flaws — is the most likely to beat Obama in November.

“I believe this is a moment that demands we return to our basic values and first principles,” Romney said. “This is our moment. This is why we are conservatives.”