Three Republican presidential candidates Friday took the stage of an important conservative gathering in Washington, trying to woo the party's base and rally support for their campaigns.

The candidates appeared throughout the day at the annual conference of the Conservative Political Action Conference (CPAC), a gathering of influential conservatives. Of the four main candidates, only Texas Congressman Ron Paul was absent as he campaigns in Maine.

First on the stage was Rick Santorum, the former Pennsylvania senator whose triple wins Tuesday night in primary and caucuses in three states had suddenly injected momentum to his campaign.

Greeted by an enthused crowd, Santorum touted his conservative credentials, and used more time attacking President Barack Obama than distinguishing himself from the rest of the field, especially Mitt Romney, the former Massachusetts governor who was long perceived as frontrunner in the race.

In his remarks, Santorum implied Romney is not a true conservative, saying if the former governor got nominated, he would lose the debate on healthcare issue to Obama. He also attacked Romney on his past support of climate change legislation and Wall Street bailout.

Romney took the stage about two hours after Santorum. Rather than the star treatment the audience gave the former senator, he received polite applauses, indicating the gap of enthusiasm conservatives feel about the two candidates.

For his part, Romney gave the audience a thorough checklist of where he stands in various issues, especially social ones, assuring them his conservative beliefs, trying to allay long standing fears that he is a moderate.

He explained his tenure as governor of the liberal Massachusetts as one that "fought against long odds in a deep blue state," adding he was a "severely conservative Republican governor."

After winning primary of Florida and caucuses of Nevada earlier this month, Romney had effectively diminished the surge of former House speaker Newt Gingrich, who beat him in South Carolina, only to see his momentum being overtaken by Santorum with triple wins Tuesday in Minnesota, Colorado and Missouri, where social conservatives have a strong presence. Romney is working hard to win over the conservatives.

Gingrich, who is regearing his campaign for a fight for next month's Super Tuesday, when 11 states will vote on the same day, took the stage in the afternoon. He used the speech to give a laundry list of what he will do if elected president, hitting every chord of conservatism including economy, foreign policy, energy, taxes and regulations.

With Romney's frontrunner status constantly being challenged, the Republican nomination contest is shaping up to be a prolonged race, with each of the candidates refusing to give up.