The GOP presidential front-runners tried to win voter sympathy in Florida Sunday by tapping into outrage over the increasingly bitter tone of the race leading to Tuesday's Republican presidential primary.

The latest poll shows a tie between Mitt Romney and John McCain , forcing the campaigns to abandon any pretense of courtesy and publicly go at one another's throats at every opportunity while still emphasizing their own resume highlights. The key points of contention are the economy and Iraq. Romney, a former venture capitalist promoting his business savvy as an asset, has been provoking McCain over past statements the Arizona senator has made acknowledging a limited expertise on the economy.

In turn, McCain is shoving in his opponent's face a comment Romney made suggesting U.S. and Iraqi leaders should set a secret timetable for U.S. soldiers to withdraw.

The former Massachusetts governor ignited a new verbal missile on Sunday, hitting his rival over the McCain-Lieberman Climate Stewardship Act, which Romney says would depress the economy, rather than stimulate it. "His plan calls for a new financial burden to be placed on people who are purchasing gasoline or, for that matter, natural gas to heat their homes or to cook in their homes. The Energy Information Agency has said that his plan would cost America 300,000 jobs. In addition, people would pay, they estimate, approximately 50 cents per gallon more for gasoline and 20 percent more for their gas utility bill," Romney told a rally of about 300 mostly Hispanic voters in Sweetwater, Fla.

"He sort of feels that maybe America should pay for global warming. Don't you understand? They don't call it America warming. They call it global warming," he said.

Click here to go to the FOX News embed blog and see Romney discussing the McCain-Lieberman bill.

But McCain launched a counter-attack on Romney's economic turf, saying the former Massachusetts governor, didn't do such a great job as executive for his state.

Gov. Romney’s record in Massachusetts shows the state "had the 3rd lowest job creation, where they had $730 million in tax increases, where they had more manufacturing jobs flee the state of Massachusetts than almost double the national average and now a health care mandate that's $245 million dollars in the red," McCain said at a town hall meeting in Polk City. "I'd be glad to compete and debate on those issues. My record on the economy is very strong -- from being part of the Reagan revolution to cut taxes and restrain spending to my latest efforts that I have been involved in as chairman of the Commerce Committee and many other economic issues."

McCain defended himself when a questioner challenged the Arizona senator's votes in 2001 and 2003 against Bush administration tax cuts. McCain now says those tax cuts should be made permanent.

"I opposed the tax cuts because I saw no restraint in the growth of spending. We let spending get out of control," he said.

The former Vietnam POW also would not back down from likening Romney to Democrats who abruptly want to get U.S. troops out of Iraq, a position the Romney campaign vehemently denies.

"The Romney campaign has been trying to interpret his remarks in a way that can’t be interpreted. The statement is quote: 'You don’t want the enemy to understand how long they have to wait in the weeds until you’re going to be gone.' ... You can only read (that) … as an endorsement of a timetable which clearly, in my view, would have lost this conflict for us and we would have paid a very heavy price in American blood and treasure. So they can interpret it any way that they want to. I believe that any objective observer would read these remarks as a support for a timetable, that in my view is simply … a message to Al Qaeda that we are leaving.”

McCain added, "Even if the economy is the, quote, number one issue, the real issue will remain America's security. ... And if they choose to say, 'Look, I do not need this guy, because he's not as good on home loan mortgages,' or whatever it is, I understand about that, I will accept that verdict. I am running because of the transcendental challenge of the 21st century, which is radical Islamic extremism."

Along with Rudy Giuliani, Mike Huckabee and Ron Paul, the two front-runners are competing in Florida for 57 delegates to the Republican National Convention in September. The winner-takes-all contest will offer strong momentum heading into the Super Tuesday contests, when more than 20 states hold nominating events on Feb. 5.

Noting the fighting, Giuliani contrasted himself with the two Sunday in both style and substance.

"Senator McCain and Governor Romney are doing such a good job of attacking each other, how about voting for somebody whose not attacking? Vote for me, Rudy Giuliani," he said while visiting the Ron Jon Surf Shop in Cocoa Beach. "Presidential election is not about name-calling. Presidential election is not about gotcha and almost, like, high school politics."

Meanwhile, Huckabee said on "FOX News Sunday that he is better equipped than his GOP rivals because he has already taken on the Clinton campaign machine and won.

"There are not two people who are better at street-fighting politics that Bill and Hillary Clinton. I've been telling people a long time, don't underestimate the scrappiness with which they'll approach this race," said Huckabee, who grew up in Bill Clinton's hometown of Hope, Ark., and served as Arkansas governor.

"The one thing you have to keep your eyes on is that tactics will change but the goal will never, ever fade. That is: win, whatever it takes to do it," he added.

Most of the candidates going into Tuesday's race claim they will come out the victor, and Romney and McCain suggested the latest round of endorsements demonstrate that their support is solid. McCain picked up the backing of Florida Gov. Charlie Crist on Saturday night, while Romney won the assistance of former Fred Thompson adviser Liz Cheney and is said to have support from a wide array of allies to former Florida Gov. Jeb Bush.

"I think it's going to give us momentum in order for us to win next Tuesday," McCain told voters in Tampa of Crist's backing.

"I've gotten great endorsements from people all over Miami and I could not be more pleased because we are going to win on Tuesday," Romney told Cuban Americans who cheered as he spoke about his effort to help a Latin American family whose son was kidnapped and killed by rebels thought to be supported by Cuban leader Fidel Castro.

FOX News' Shushannah Walshe and Malini Bawa and The Associated Press contributed to this report.