WASHINGTON (AP) - A resurgent Rick Santorum won Republican presidential caucuses in Minnesota and Colorado on Tuesday night, a stunning sweep that raised fresh questions about front-runner Mitt Romney's appeal among the ardent conservatives at the core of the party's political base.

Santorum triumphed, as well, in a nonbinding Missouri primary that was worth bragging rights but no national convention delegates.

"Conservatism is alive and well in Missouri and Minnesota," the jubilant former Pennsylvania senator told cheering supporters in St. Charles, Mo. Challenging both his GOP rival and the Democratic president, he declared that on issues ranging from health care to "Wall Street bailouts, Mitt Romney has the same positions as Barack Obama."

Returns from 83 percent of Minnesota's precincts showed Santorum with 45 percent support, Texas Rep. Ron Paul with 27 percent and Romney - who won the state in his first try for the nomination four years ago - with 17 percent. Former House Speaker Newt Gingrich trailed with 11 percent.

It was closer in Colorado, where returns from all the precincts showed Santorum with 40 percent of the vote to 35 for Romney. Gingrich had 13, and Paul claimed 12 percent.

Romney showed no sign of disappointment in remarks to supporters.

"This was a good night for Rick Santorum. I want to congratulate Sen. Santorum, but I expect to become the nominee with your help," he told supporters in Denver.

If the night was good for Santorum, it was grim for Gingrich, who made scant effort in any of the states that voted during the day. He ran far off the pace in both caucus states, forced to watch from the sidelines while Santorum boasted of being the candidate with conservative appeal.

There were 37 Republican National Convention delegates at stake in Minnesota and 33 more in Colorado, and together, they accounted for the largest one-day combined total so far in the race for the GOP nomination.

The victories were the first for Santorum since he eked out a 34-vote win in the lead-off Iowa caucuses a month ago, and he reveled in the moment. "I don't stand here to be the conservative alternative to Mitt Romney. I stand here to be the conservative alternative to Barack Obama," he told his supporters.

He had faded far from the lead in the primaries and caucuses since, and Gingrich seemed to eclipse him as the leading conservative rival to Romney when he won the South Carolina primary late last month.

While Romney throttled back after victories in Florida and Nevada in the past several days, Santorum campaigned aggressively in all three states on the ballot, seeking a breakthrough to revitalize his campaign.

He won Minnesota largely the way he did Iowa, dispatching his organizers from the first state to the second and courting pastors and tea party leaders alike.

Romney's campaign moved swiftly to take the sting out of the Missouri vote. The state's Republican Sen. Roy Blunt, a Romney supporter, congratulated the winner but noted the state's delegates are still up for grabs. He said, "Mitt Romney has the organization and the resources to go the distance in this election, and I believe he'll ultimately win our party's nomination."

And it was not clear where Santorum could exploit his victory. Aides have already said he has little hope in Maine caucuses that end this weekend, the next event on the calendar.

Paul, a Texas lawmaker, has yet to win a primary or caucus. He claimed credit for a strong second-place finish in Minnesota and said he was optimistic about his chances in Maine.

Romney began the day the leader in the delegate chase, with 101 of the 1,144 needed to capture the nomination at the Republican National Convention this summer in Tampa. Gingrich had 32, Santorum 17 and Paul nine.

Though the delegate total on Tuesday was high, the campaigning was a pale comparison to the Iowa caucuses or primaries last month in New Hampshire, South Carolina and Florida.

Television advertising was sparse; neither Colorado nor Minnesota hosted a candidates' debate, and there was relatively little campaigning by the contenders themselves until the past few days.

The same was true in last weekend's Nevada caucuses, which Romney won on the heels of a Florida primary victory days earlier. The same pattern holds in Maine.

Not until primaries in Michigan and Arizona on Feb. 28 is the campaign likely to regain the intensity that characterized the first few weeks of the year.

Then it roars back to life with a 10-state Super Tuesday on March 6 with 416 convention delegates at stake. Georgia, where Gingrich launched his career in Congress, is the biggest prize that night with 76 delegates. Next is Ohio, which has 63 delegates at stake and where early voting has already begun.

Santorum, in particular, was eager to seize the relative lull to redeem the promise of his Iowa victory.

He campaigned more aggressively this week than any of the other contenders, and he spent Tuesday hopscotching from Colorado to Minnesota to Missouri in hopes of nailing down at least one victory. Touting himself as a true conservative - a slap at Gingrich - he sought to undermine Romney's electability claim at the same time by predicting the former Massachusetts governor would lose to Obama.

Romney responded by assailing Santorum as an advocate of congressional earmarks - shifting the criticism he had leveled at Gingrich when the Georgian seemed a more imposing threat.

In the hours before the caucuses convened, the front-runner sought to lower expectations.

"Mitt Romney is not going to win every contest," Rich Beeson, the campaign's political director, wrote in a memo for public consumption.

"John McCain lost 19 states in 2008, and we expect our opponents will notch a few wins, too," Beeson wrote. McCain, the Arizona senator, won the Republican nomination four years ago.

In fact, Colorado and Minnesota were among the states that McCain failed to win, and he lost them to Romney.

In the four years since, the GOP has become more conservative in both. That posed a challenge for Romney, who runs as the Republican most likely to defeat Obama and is still trying to establish his credentials among tea party activists suspicious of a one-time moderate who backed abortion rights.

Two years ago in Minnesota, establishment candidates for governor were swept aside in the primary, and tea party-backed insurgents for governor and the Senate in Colorado won the party nominations.

In Romney prevailed in both Minnesota and Colorado in 2008, the first time he ran for the nomination, but the GOP has become more conservative in both states since then under the influence of tea party activists. And he lacked the overwhelming advantage in television advertising, including fiercely negative attacks on his rivals, that had helped him in other states this year.

Gingrich spent the day campaigning in Ohio, one of the primary states on March 6.

His campaign went into a downward spiral after he won the South Carolina primary in an upset. The former speaker was routed in the Florida primary to Romney, then finished a distant second in Nevada over the weekend. all three cases, Democrats won in the general election that fall.