WASHINGTON - Newt Gingrich once led his rivals for the nomination in polls. Today, the former House speaker is millions in debt and describing Mitt Romney as "far and away the most likely" GOP presidential nominee. Running for president "turned out to be much harder than I thought it would be," he said Sunday.

"I do think there's a desire for a more idea-oriented Republican Party, but that doesn't translate necessarily to being able to take on the Romney machine," Gingrich told "Fox News Sunday" in a reflective interview.

After his Jan. 21 victory in the South Carolina primary, Gingrich said the Florida primary he lost in the following days turned into a "real brawl." He said Romney did a good job building a substantial machine, adding he has no regrets.

"Unfortunately, our guys tried to match Romney," Gingrich said of the Florida matchup. "It turned out, we didn't have anything like his capacity to raise money."

Gingrich said he has a little less than $4.5 million in campaign debt, and he's operating on a shoestring budget.

Despite his acknowledgment of what appears to be his inevitable defeat, he isn't ready to drop out. Gingrich wants to influence the party's platform, which is a statement of principles on the issues. He's interested in promoting increased domestic oil production and personal Social Security savings accounts.

But, if Romney secures the nomination, Gingrich said he'll campaign for him.

ASSOCIATED PRESS