BY BETH REINHARD, LAURA FIGUEROA AND PATRICIA MAZZEI

John McCain, the Vietnam War hero who has doggedly championed the war in Iraq, told a roaring crowd of about 6,000 people in Miami on Friday that he would not stop battling for his country -- and the presidency.

The Republican nominee used the word ''fight'' at least 20 times in his speech. Relishing his position as the underdog, McCain was more animated than he has appeared in recent weeks on the campaign trail in Florida, and the pompom-shaking crowd was one of the loudest.

''What America needs now in this hour is a fighter, someone who puts all his cards on the table and trusts the judgment of the American people,'' McCain said, standing in front of a ''VICTORY'' banner at the packed Florida International University Arena. ``I come from a long line of McCains who believed that to love America is to fight for her.''

McCain's visit to a heavily Republican corner of Miami-Dade was aimed at mobilizing Florida's largest county in the waning days of the race. Democratic nominee Barack Obama is slated to campaign in Miami on Tuesday, following appearances to promote the start of early voting on Monday in Tampa and Orlando.

Most polls since late September have shown Obama running ahead of McCain in Florida, the state that leads to the White House.

Florida's importance to both campaigns has crystalized in recent days, with the visits from both candidates underlining Miami-Dade's critical role. At least four top Obama campaign strategists, including the national Hispanic vote director, will be in Florida for the homestretch, seeking to close the deal. Deputy Campaign Manager Steve Hildebrand is dedicated solely to Miami-Dade, where he is focused on increasing turnout among the county's more than 500,000 Democrats.

''If we dramatically improve performance in Miami-Dade, we win Florida,'' Hildebrand said.

Former Democratic nominee John Kerry's margin of victory in Miami-Dade in 2004 was only about 50,000 votes.

OBAMA'S STRATEGY

The Obama campaign is also aiming to surpass the benchmark in the heavily Republican Cuban-American community set by President Clinton in 1996, when he won roughly 36 percent of those voters. Obama has sought to appeal to younger and more moderate Cuban-Americans by calling for unfettered travel and remittances to the island, but Republicans say his platform will backfire.

''People keep asking me if things have changed in Miami,'' Cuban-American Sen. Mel Martinez, a Republican, told the predominantly Hispanic audience before McCain spoke. "I know that Miami, that Miami-Dade County, the Cuban vote, is going to be solidly Republican.''

Having watched his poll numbers plunge along with the economy in recent weeks, McCain delivered the classic conservative pitch of lower taxes and spending in speeches in Miami and later in Melbourne. Arguing that Obama would raise taxes on ordinary, working people, McCain continued the ''Joe the Plumber'' line of attack he began at Thursday's debate, though he renamed him "José el Plomero.''

McCain said of his opponent: "Not only did he vote for higher taxes on the middle class in the Senate, his plan gives away your tax dollars to those who don't pay taxes. That's not a tax cut; that's welfare.''

The Obama campaign responded: "John McCain again distorted Sen. Obama's tax proposal today, labeling as welfare the tax relief Barack Obama wants to give millions of line workers, teachers, plumbers and other middle-class Americans who pay payroll taxes on every dollar they earn.''

McCain also accused Obama of wanting to force voters into ''a new huge government-run healthcare program that keeps the fine a secret until it hits you with it,'' a claim some fact-checking groups have dismissed.

In a counterattack, Obama is running a new ad in Florida in which Florida Democratic Sen. Bill Nelson says McCain will slash Medicare and Medicaid funding.

After leaving Miami, McCain addressed a crowd of about 1,700 in Melbourne, a heavily Republican area where many people working in the nation's space program face an uncertain future.

McCain did not mention William Ayers, the bomb-throwing Vietnam War protester who hosted a fundraiser for Obama in 1995. But national media have reported that the campaign is deluging at least 10 battleground states, including Florida, with automated phone calls that accuse Obama of working with a "domestic terrorist.''

At FIU, campaign volunteers ran up and down the bleachers blowing whistles and waving banner-sized American flags to excite the crowd. At the mention of the Democratic nominee by Jim Greer, the state's Republican chairman, the packed arena booed loudly.

A handful of voters at recent rallies for McCain and running mate Sarah Palin have shouted threats and obscenities, and Greer tried to send a message to the Miami crowd by calling Obama an ''honorable man.'' Still, he added, "there is nothing wrong with talking about judgment and character.''

Outside the arena, drivers who passed by about a dozen Obama supporters shouted "Communists!''

RECENT POLLS

Statewide, a new SurveyUSA poll showed McCain ahead by two percentage points in an essentially tied race. However, a Hamilton Campaigns survey also released Friday found Obama ahead 47-43 percent and noted that McCain led by only 11 percentage points in the conservative Panhandle and Northeast Florida.

''Voters concerned about the economy are lost to McCain, and without increased support in the Panhandle, there's no way for McCain to win Florida,'' said Democratic pollster David Beattie.

But Gov. Charlie Crist, a Republican who has faced questions recently about whether he was distancing himself from McCain as the nominee's poll numbers dropped, cautioned the crowd at the McCain rally: "Never count John McCain out. Never count John McCain out.''

McCain's spirited speech resonated with voters like Julio Regalado, 70, and Raul Perez, 72, who said they skipped their daily trek to Versailles restaurant in Little Havana to attend the rally.

''He shows that he's a grand patriot and hero unafraid to defend us,'' Regalado said.

"That's the type of president you want on your side, the type who is willing to fight for the people.''

Miami Herald writer Vanessa A. Alvarez contributed to this report.