GREENVILLE, S.C. --- With his Republican rivals jockeying for victory in New Hampshire, presidential hopeful Fred Thompson sought Tuesday to boost his support in this early voting state considered critical to his campaign.

"I don't know of any better place to stand my ground and test my case than in South Carolina," Mr. Thompson told a couple of hundred people at a pancake house in the northern part of the state as he began an 11-day bus tour.

Several hours later, he said primary results in New Hampshire and in Michigan on Jan. 15 will factor into whether he stays in the race -- but that South Carolina will be key.

"This is where we make our stand -- this is where I have chosen to make my stand," Mr. Thompson told a crowd at a barbecue restaurant. He later told reporters he needs to do well in South Carolina, which votes Jan. 19.

"There's no question about it. It could prove at the end of the day that South Carolina is determinative as far as I'm concerned, but we're not there yet," he said.

In November, one state poll had the former Tennessee senator in a virtual tie for the lead in South Carolina with former New York Mayor Rudy Giuliani and former Massachusetts Gov. Mitt Romney. A month later, eventual Iowa caucus winner Mike Huckabee came on strong, leading or sharing the top spot in three other surveys.

A New Hampshire poll out this week showed Mr. Thompson in low single-digits there. Analysts and even Thompson supporters say he must do well in the Republican primary in South Carolina to continue a viable campaign through Feb. 5, when more than 20 states hold primaries or caucuses.

The urgency is not lost on either the candidate or his backers. On Tuesday, Thompson supporter Chris Rush asked the candidate how to gain more media attention.

"Win South Carolina," Mr. Thompson shot back.

The bus tour strategy worked well for Mr. Thompson in Iowa, where he finished ahead of the fourth- or fifth-place slot that had been predicted, said Thompson campaign spokesman Jeff Sadosky. A good finish in South Carolina, Mr. Sadosky said, could help boost Mr. Thompson's prospects Feb. 5.

"It's going to be important, and I think the focus that we're giving to South Carolina is a good tell of just how important it is to us," Mr. Sadosky said Monday.

Recent polls in South Carolina show Mr. Huckabee leading, with Mr. Thompson's support tough to read. In one survey, he placed second; in two others, he placed fourth and fifth.

Brenda Muckenfuss, a 47-year-old Lexington resident, said she's long supported Mr. Thompson.

"I feel like he's the one candidate who has the courage to tell it like it is," she said. "I just wish he'd announced a little sooner."

But some who attended Mr. Thompson's appearances Tuesday said they were still making up their minds.

"We like what he says and how he says it," said Carole Crow. But she said she was leaning to Arizona Sen. John McCain or Mr. Romney. "You feel like you want to support somebody who can make it all the way," she said.

On Tuesday, Mr. Thompson answered questions on foreign policy. Asked about Iran as a nuclear threat, he said it is difficult to rely on intelligence reports that say the country has ended its nuclear weapons program.

He also joked about leaving behind his rivals and New Hampshire's colder climate for South Carolina, where temperatures are forecast in the 70s this week.

"So I ask you, who's the smartest one?" Mr. Thompson said.