WASHINGTON — Republican presidential rivals made contrasting appeals to conservatives on Friday, with Mitt Romney saying he proved his mettle as Massachusetts governor and Rick Santorum saying Romney is too moderate.

Their speeches to the Conservative Political Action Conference came as Santorum tries to convert his surprising caucus wins this week into a resilient, muscular campaign and Romney seeks to persuade conservatives that he won't disappoint them.

The winner of the Republican contest will face Democratic President Barack Obama, who will seek re-election next November.

Santorum, a former Pennsylvania senator, called on the Republicans to put a conservative crusader into the White House.

"We will no longer abandon and apologize for the policies and principles that made this country great for a hollow victory in November," he said.

If voters see that as a hint that it's more important to be ideologically pure than to oust Obama, Santorum may have to explain more fully in the days ahead.

Romney, speaking a few hours later, said his four-year record in Massachusetts proved that he will fight for conservative values against the toughest odds.

"I know conservatism because I have lived conservatism," he said. Veering briefly from his written text, he called himself "severely conservative."

But Romney skated past details of his administration that trouble some right-leaning groups, including requiring state residents to obtain health insurance.

Without saying Romney's name, Santorum said the former governor's health care record would make it impossible for him to draw needed contrasts with Obama. He said Romney had created "the stepchild of Obamacare."

Saying the Obama-backed 2010 health care law "will crush economic freedom," Santorum urged Republicans not to nominate "someone who would simply give that issue away in the fall."

Republican Newt Gingrich, the former speaker of the U.S. House, also was to address the conservative gathering in Washington.

It comes after Santorum won three election contests this week -- a reminder that the race to challenge Obama remains far from settled.

Santorum has far less money and campaign organization than the very wealthy Romney, who has been running for president for years and dropped out of the 2008 race.

Romney has won contests in New Hampshire, Florida and Nevada. He lost South Carolina to Gingrich last month.

But Santorum's wins in the Colorado and Minnesota caucuses this week, plus a nonbinding primary in Missouri, have raised questions once again about front-runner Romney's ability to inspire conservatives. Santorum earlier won Iowa.

In his speech to the annual Conservative Political Action Conference on Friday, Santorum cast himself as the candidate who will allow true conservative voters to keep their "honour" and stay true to their principles. He didn't mention Romney by name but referred to him as the candidatewith "the most money to beat up their opponent and win the election."

Rep. Ron Paul, whose libertarian leanings put him at odds with some mainstream conservatives, does not plan to attend Friday.

The CPAC appearances come one day before Maine's caucus results will be announced. Many Republicans expect Paul to do well there.

The far more important primaries in Michigan and Arizona follow on Feb. 28. After that comes the delegate windfall available on so-called Super Tuesday, when 10 states vote March 6.