ORLANDO, Fla. — Mitt Romney and John McCain are in an increasingly bitter and personal struggle to control the campaign conversation before Florida's primary on Tuesday — and the Republican presidential nomination itself may go to the one who succeeds.

Romney, the former Massachusetts governor and venture capitalist, casts himself as a business-savvy economic turnaround artist amid recession anxiety, while McCain, the Arizona senator and Vietnam veteran, portrays himself as a courageous wartime commander in chief in a dangerous world.

"He has an enormous disadvantage when it comes to the topics of changing Washington or fixing our economy," Romney said Sunday, arguing that he is far stronger than McCain on both issues.

Countered McCain: "Even if the economy is the, quote, No. 1 issue, the real issue will remain America's security" — and, unlike him, Romney is deficient in that area.

The two leaders for the Republican nomination essentially are beginning their national arguments here, ahead of a virtual national primary on Feb. 5. They are giving rank-and-file GOP voters a choice between what have historically been the party's two most important issues — the economy and national security. That's not an easy decision for many Republicans.

Rudy Giuliani, the former New York mayor trying to salvage his candidacy, has been arguing that he offers a perfect combination — strength on the economy and on security — and is hoping to benefit from their squabbling. "Senator McCain and Governor Romney are doing such a good job of attacking each other, how about voting for somebody who's not attacking? Vote for me, Rudy Giuliani," he said in Cocoa Beach, Fla.

In the past month, the economy has replaced national security as the top concern among Republican voters as financial market turmoil and a housing crisis prompted President Bush to push an economic stimulus package to prevent a recession.

The shift works in Romney's favor and against McCain.

So, Romney has spent the past week promoting his private-sector credentials and arguing that McCain, who has served the country in the military and in Congress for most of his adult life, lacks economic know-how and qualifications as the country teeters on the brink of recession.

McCain, in turn, has sought to resurrect the national security issue by trumpeting his decades-long experience on defense issues while arguing that Romney doesn't have the judgment needed in wartime. In a misleading attack, McCain also accused him of once wanting a timetable like the Democrats wanted for troop withdrawals.

Their intense fight underscores the extraordinarily close Florida race and the stakes at hand. Polls show them battling for the lead in the state, which offers the winner a hefty 57 delegates to the party's nominating convention and momentum heading into the Feb. 5 contests.

Long a muddle, the GOP nomination race has narrowed into a two-man contest between Romney and McCain.

Giuliani has lost six straight contests. He has pinned his candidacy on a Florida win but is badly trailing and is facing money woes. Mike Huckabee, the former Arkansas governor, won the leadoff Iowa caucuses but hasn't prevailed since and is all but broke, barely playing in Florida.

Romney won his native state of Michigan and two scarcely fought contests in Wyoming and Nevada. He needs a Florida victory to prove he can win in a hard-fought state and in a place where he doesn't have roots.

McCain, who scored big wins in New Hampshire and South Carolina, wants Florida to cement him as the clear front-runner.