CHARLESTON, South Carolina — Republican frontrunner Mitt Romney hit a roadblock Sunday in South Carolina as Christian conservative leaders coalesced behind Rick Santorum in the race for the presidential nomination.

A group of 155 Christian evangelical leaders from around the country endorsed Santorum, a former Pennsylvania senator, Saturday after holding a vote on a Texas ranch to agree on a single candidate before the January 21 South Carolina primary.

"It's a big hit, let's be honest," Senator John McCain, who recently endorsed Romney, said on CNN. "There's a very strong evangelical movement in South Carolina, particularly inland."

The move by the Christian right brought to the surface an undercurrent of alarm, if not outright hostility, among some evangelical Christians over the prospect of a Mormon being nominated to run against President Barack Obama in November.

That hurdle to Romney's nomination has come into sharper relief as the Republican race has moved out of the northern states into the Bible Belt, where religion and politics often make for a volatile mix.

Candidates passed over by the Christian right scrambled to paper over their loss, saying they believed the fight would be on the economy in a state with high unemployment that has struggled to emerge from recession.

"The one consensus was nobody was for Mitt Romney," said Gingrich, running a close second in the polls, on NBC's Meet the Press, adding he had strong support from conservatives.

But Gingrich, who represented neighboring Georgia in Congress, acknowledged that the bloated Republican field helps Romney.

"The only way a Massachusetts moderate can get through South Carolina is if the vote is split, but we have six days to make our case to people," he said.

Gingrich and other rivals kept their attacks trained on Romney's record as a former venture capitalist who they say destroyed thousands of jobs during lucrative corporate takeovers.

The attacks, including Texas Governor Rick Perry's graphic depiction of venture capitalists as vultures waiting to swoop in and devour weakened companies, have unsettled some establishment Republicans who complain they are playing Obama's game for him.

"The fact is, if this is a fatal flaw, we need to be talking about it now, not talking about it in September and October," Perry told CNN.

Gingrich echoed that line in an interview with CBS's Face the Nation, saying, "It?s fair to raise the questions now, get them out of the way now to make sure that whoever we nominate is clear enough, public enough, accountable enough that they can withstand the Obama onslaught."

The candidates face off in two debates ahead of Saturday's crucial South Carolina vote -- the first Myrtle Beach on Monday and the second in Charleston on Thursday.

Surveys show Romney leading the field in South Carolina with 26.7 percent support, according to Real Clear Politics, a website that aggregates poll numbers. He is followed by Gingrich at 22 percent, Santorum at 14.7 percent, Ron Paul at 14.7 percent, and Perry tied with Huntsman at 5.7 percent.

Huntsman picked up an endorsement from South Carolina's largest newspaper, the State, while Romney garnered endorsements from the Greenville News and the Charlotte (North Carolina) Observer.

"We'll just have to see how this plays out," said Perry, who has aggressively courted the evangelical vote but was passed over by evangelical leaders.

"It's going to be interesting with the economy like it is, and there are a lot of people who are social conservatives who realize they've got some choices in this race. But the economy of South Carolina is suffering. They're almost at 10 percent unemployment.

"So I think there is a very deep focus on who is it that can get this country back on track from the standpoint of economics."

Romney is the strong favorite for the Republican presidential nomination after eking out a narrow win in Iowa on January 3 and notching up a clear victory in New Hampshire the following week.