Tuesday's primary, coming only a week before the tsunami of states voting Feb. 5, could give a major boost to either John McCain or Mitt Romney, who appear to be the duo battling it out for their party's nomination.

Polls show McCain and Romney neck and neck, with other rivals, Mike Huckabee and Rudy Giuliani, fighting it out for third and fourth place.

The Sunshine State's primary offers the best opportunity for either McCain or Romney to take the spotlight going into the 22-state contest on Feb. 5, a day with more than 1,000 Republican delegates at stake in a contest where 1,191 are needed to get the nomination.

"It's going to really send a signal for Super Tuesday," says Maurice Carroll, director of the Quinnipiac University Polling Institute in Connecticut. "Without question, Florida will set the stage."

Florida's primary is a key test of support among conservatives.

The state's GOP primary is the first in the process that is closed to non-Republican voters. Those with any other party affiliation, or who describe themselves as independents, won't get to participate in Florida's Republican primary.

That could be bad for McCain, who has seen support from moderates and independents as he seeks the White House. But the Arizona senator just got a boost from winning the South Carolina primary, loads of news coverage and the cover of Time magazine. And he is looking at Florida for more.

David Twigg, a professor of political science at the University of Florida, says he is not sure how big of a bounce a candidate could get from taking the state's primary heading into Feb. 5's big primary.

"Different candidates have different strengths," Twigg says, and it's hard to predict what may happen after Florida.

"McCain will win in some states, Romney will win in some, Huckabee could win in some,'' Twigg says. "I can't predict anything."

One potential forecast, though, is the downfall of Giuliani. The candidate has staked almost his entire effort in Florida, but is now coming up third or fourth in polls. Political observers say it may be one of the most dramatic declines of a candidate once leading national polls and thought a front-runner for the GOP nomination.

But Giuliani skipped the early states of Iowa, New Hampshire and Michigan, losing valuable media attention, and has had a tough time competing against McCain's party status and Romney's personal fortune.

"I never really understood Giuliani picking a fight with a man who has a bottomless checkbook in a state with 13 media markets," says Tom Eldon, a partner at the polling firm Schroth, Eldon and Associates, which surveyed Florida voters on their presidential picks.

For Giuliani, Florida could dim any chances he has at winning the White House. Conversely, it could supercharge McCain or Romney's efforts.

A McCain win, coming after high-profile victories in New Hampshire and South Carolina, could almost assure him several more states on Feb. 5 and, in the end, the GOP crown. "It gives him a huge bounce," Eldon says.

But if Romney takes Florida, the campaign bump he gets could help Romney secure his ground as the conservative candidate, Eldon says, and other states may be receptive to that pitch.

MSNBC's political director, Chuck Todd, writes in his online column that Florida presents a chance for Romney or McCain to get a huge lift from a victory only days before about half the nation gets a chance to vote.

Florida could be good for Romney, he says, because it is a friendly electorate there.

"Couple that with the shift of focus from the war to the economy and Romney's got his chance," Todd says, noting Romney's credentials as a businessman who can turn around bad situations.

"As for McCain," Todd adds, "Florida also presents his best chance to become the nominee. A win here and this race is over."

McCain leads in many of the heavily populated Northeastern states, where the victor takes all delegates up for grabs, Todd notes, and those leads in delegate-rich New York, New Jersey and Connecticut will be cemented for McCain if he wins Florida.

Of course, Romney also has a good chance of taking several states on Feb. 5, including Utah where he pulled about $4.6 million from donors in only nine months last year. Plus, Romney is competitive in several counties in California, a state where candidates can win delegates by congressional district.

tburr@sltrib.com