"I don't think we can win in Wisconsin, but I think we can do very well in Wisconsin," the former U.S. senator from Pennsylvania said at a breakfast with a small group of reporters in Washington Monday.
Wisconsin, with 42 delegates, holds its primary April 3. Maryland, with 37 delegates, and the District of Columbia, with 19, hold their primaries the same day.
Santorum told reporters he thought he would do well in his home state of Pennsylvania when it holds its primary April 24 and in eight other states holding primaries in May, The Washington Examiner reported.
A few minutes after saying he didn't think he'd win Wisconsin, Santorum denied he said it.
"I didn't say that," Santorum said. "I think we can."
When reporters insisted he'd said he didn't think he'd win, Santorum said: "OK, let me pull that back. I said I'm not sure that we can win Wisconsin, obviously being outspent [by front-runner Mitt Romney], but let me pull that back.
"I do think we can win Wisconsin," he said. "I'm not saying we will win Wisconsin, but we're putting a lot of time and energy in Wisconsin. ... Yes, I think we can be competitive there, and we might be able to pull it off. It won't be easy, but I think we can pull it off."
Romney -- in California Monday and Tuesday in a blitz to raise money for his campaign against Santorum, former U.S. House Speaker Newt Gingrich of Georgia and U.S. Rep. Ron Paul of Texas -- called President Barack Obama's healthcare overhaul being argued before the Supreme Court "an attack on free enterprise, an attack on economic freedom unlike anything we have ever seen before."
"We've got to make sure that we replace President Obama with someone who truly understands what it is that makes America's economy work," he said, as he stood before a "Repeal and Replace Obamacare" banner at a San Diego medical-device manufacturer.
Romney has defended the healthcare mandate he signed as Massachusetts governor, calling it an appropriate statewide approach and saying it does not resemble the U.S. Patient Protection and Affordable Care Act Obama signed March 23, 2010.
Gingrich defended his decision to stay in the GOP presidential race despite his poor showing to date -- he has 126 fewer delegates than Santorum and 433 fewer than Romney.
He told CNN, "If Romney can't clinch it, I think it becomes pretty wide open."
He claimed Santorum "doesn't have a guaranteed lock" on the race any more than he or Romney do.
"I think the morning that [Romney] gets 1,144 that are locked down, then I think he can claim to be the nominee. But until then, he's not the nominee," Gingrich said.
"Remember, I'm from Atlanta, where we [the Atlanta Braves baseball team] were ahead by 10.5 games last year with only 28 games to go, and the [St. Louis] Cardinals didn't quit," he said. "Everybody wanted them to, but they just kept coming and they ended up winning. I think this is not over until it's over."
Paul said voters should not dismiss his candidacy simply because he lags far behind in the fight for the Republican presidential nomination.
"Our people are in the right places. They're doing the things to become delegates," Paul told CNN, adding it was too soon to "write anybody off."
Paul has 71 delegates, Gingrich has 136, Santorum has 262 and Romney has 569, CNN reported.