OXON HILL, Md. — Republican Mitt Romney told conservative activists Friday that he's sorry he's not their president but promised to work alongside them to help strengthen the Republican Party.

"Each of us in our own way will have to step up and meet our responsibility," Romney told a crowd at the Conservative Political Action Conference, a three-day political summit in suburban Washington.

"I am sorry that I will not be your president," the 2012 Republican presidential nominee said during his first public speech since the election loss. "But I will be your co-worker, and I will work shoulder-to-shoulder alongside you."

Romney's conservative credentials were sometimes questioned during his presidential campaign, but he was greeted with a roaring ovation and interrupted by applause several times during his brief remarks. Advisers said his appearance was designed to thank conservatives for backing him.

Romney won the conference's straw poll one year ago, when he described himself as "severely conservative."

The former Massachusetts governor is not expected to play a leading role in the future of the Republican Party, but he said, "It's up to us to make sure that we learn from our mistakes, and my mistakes."

He encouraged conservatives to study the successes of the nation's 30 Republican governors and praised the "clear and convincing voice" of his former running mate, Wisconsin Rep. Paul Ryan, who spoke in the same ballroom earlier.

"Of course, I left the race disappointed that I didn't win," Romney said. "But I also left honored and humbled to have represented the values we believe in and to speak for so many good and decent people."