Rick Santorum said today that the Republican presidential fight is "a three-person race," and he is the better conservative bet against President Obama than either Mitt Romney or Newt Gingrich.

"The real conservative has yet to emerge -- and that's me," Santorum said on CNN's State of the Union.

During the interview, Santorum disputed Gingrich's claim that he is "the only practical conservative vote" to stop Romney, the "Massachusetts moderate."

Instead, Santorum -- who on Saturday was formally declared the winner of the Iowa caucuses -- challenged Gingrich's conservatism on several fronts.

He noted that Gingrich has backed requirements that all Americans buy health insurance, "bailouts" for Wall Street, legislation on global warming legislation and guest worker programs for illegal immigrants.

In an interview on ABC's This Week, Santorum said "a lot of conservatives are very concerned about the choice" between Romney and Gingrich.

"In their opinion, and in mine, that's not a choice between a conservative and a moderate," Santorum said. "It's a choice between a moderate and an erratic conservative, someone who on a lot of the major issues has been just wrong."

Santorum, the Iowa winner, noted that South Carolina is in Gingrich's "backyard" because he is from neighboring Georgia; he also pointed out that Romney won the primary in his neighboring state, New Hampshire.

The next GOP primary: Florida, on Jan. 31.

"We're now going to go on neutral turf," Santorum said.