U.S. Republican Newt Gingrich scrambled to revive his fading hopes in Florida on Monday, lashing out at rival Mitt Romney as a liberal party insider the day before the state's crucial presidential primary.

Polls showed Romney with a commanding lead in the state, where Gingrich's attacks on the former head of a private equity firm as an elite friend of Wall Street have failed to make an impression with Republicans who cast ballots on Tuesday.

Gingrich kept up the offensive on the campaign trail and in television interviews on Monday, pledging to stay in the White House race for the long haul and insisting Republicans eventually would rally to his candidacy.

On big philosophical issues, he is for all practical purposes a liberal and I am a conservative and that's what this fight is going to be about all the way to the convention, he said of Romney on CBS This Morning.

A win in Florida would be a vital boost for Romney, who was backed last week by several prominent conservatives and party leaders worried a Gingrich nomination would doom Republicans in the general election against President Barack Obama.

Gingrich said heavy spending by Romney, the former Massachusetts governor, and the Super PAC that supports Romney had killed the momentum Gingrich built with a double-digit win over Romney on January 21 in South Carolina.

He can bury me for a very short amount of time with four or five or six times as much money, most of it raised in Wall Street from the guys who got bailouts from the government, Gingrich said on ABC's Good Morning America.

A Quinnipiac University poll of likely Florida voters released on Monday indicated Romney has a 14-point advantage over Gingrich with broad-based support from across the Republican coalition including self-described conservatives, white evangelical Christians and Tea Party supporters.

Other polls also have shown Romney opening up a double-digit lead on Gingrich, the former speaker of the U.S. House of Representatives.

If this margin holds up tomorrow, it's hard to see where Gingrich goes from here, Quinnipiac pollster Peter Brown said.

But the Gingrich campaign worked to spread the idea he was staying in the race long-term. This race is just getting started, Martin Baker, Gingrich's national political director, said in a memo to reporters.

At least 1,114 delegates are needed to secure the Republican nomination in August. Florida is the largest state to hold a presidential primary so far this year, and 50 delegates are at stake in a winner-take-all format that will decide who faces Democratic President Barack Obama in November.

'LONG WAY TO GO'

But Baker said even a Romney win in Florida will give him just 7 percent of the delegates needed to claim the nomination. The next contest after Florida will be Nevada on Saturday, followed by Minnesota, Colorado and Missouri on February 7.

There is a long way to go before either candidate clinches the nomination, and this campaign will continue for months, he said. The campaign is shifting to a new phase where opportunities are not limited to a single state.

Talking to reporters on Monday, Romney noted Gingrich's growing interest in the campaign's long haul.

That's usually an indication that you think you're gonna lose. When you say 'I'm gonna go on no matter what happens,' that's usually not a good sign, Romney said.

Gingrich said opposition to his candidacy by party insiders was a badge of honour and a sign of how threatening his candidacy was the elite.

They recognize I'm a genuine outsider. I know a lot about Washington having served as speaker but have none of the establishment ties and I will shake the system up. They don't want to be shaken up, he said on CBS.

Both candidates crisscrossed Florida in a final hunt for votes on Monday. The two other remaining Republican contenders, former U.S. Senator Rick Santorum and U.S. Representative Ron Paul, are looking beyond Florida to the next races in Minnesota, Colorado and Nevada.

After bickering with Romney over which of them was best suited to extend former President Ronald Reagan's legacy of conservatism, Gingrich brought Reagan's son, Michael, with him on the campaign trail on Monday to bolster his case.

Gingrich said Reagan's presence should end questions from the party establishment about his links to Reagan.

I figured if his son was prepared to campaign with me, for anybody with an open mind, that should settle that issue once and for all, Gingrich said in Jacksonville.

Reagan said he owed Gingrich a campaign appearance because of what he's done for the Republican Party over the years. I remember him back in the 1980s during the Reagan revolution.

(Additional reporting by Sam Youngman, Susan Heavey; Writing by John Whitesides; Editing by Mary Milliken and Doina Chiacu)