Democrat Barack Obama hit White House rival John McCain with a prime-time TV onslaught, vowing to remake US fortunes at home and abroad, as the Republican countered with caustic character attacks six days from election day.

Obama delivered a 30-minute campaign pitch on national television on Wednesday, ending with a live cut to the thumping climax of a rally attended by 20 000 supporters, on the final stretch of his bid to be America's first black president.

The ad, which aired on three networks before a World Series baseball game at a cost of at least three million dollars, featured patriotic tropes, intensely personal moments and stories of real Americans struggling to make ends meet.

American Dream for all

The 47-year-old Democrat, promoted in the broadcast as a loving family man who overcame hardship to reach the pinnacle of politics, pledged to remake the American Dream for all and safeguard the nation from foreign threats.

"We've seen over the last eight years how decisions by a president can have a profound effect on the course of history — and on American lives," he said to camera, after shots of rolling wheat fields and the US countryside.

"But much that's wrong in our country goes back even farther than that. We've been talking about the same problems for decades — and nothing is ever done to solve them," Obama said.

"This election is a defining moment. The chance for our leaders to meet the demands of these challenging times and keep faith with our people," he said.

"But everywhere I go, despite the economic crisis and war and uncertainty about tomorrow, I still see optimism. And hope. And strength."

McCain was unimpressed.

"When you're watching this gauzy, feel-good commercial, just remember that it was paid for with broken promises," he said, attacking Obama's decision to opt out of public campaign financing.

En route to two rallies in the coveted prize of Florida, including his first joint event with former president Bill Clinton at midnight in Orlando, Obama said a vote for McCain would cripple the middle class and reward fat cats.

Addressing 28 000 supporters in Raleigh, North Carolina, Obama also derided his Republican opponent's attacks on his own tax proposals as "socialism".

"By the end of the week, he'll be accusing me of being a secret communist because I shared my toys in kindergarten," he said.

McCain renews character attacks

McCain (72) was also campaigning in Florida where he renewed his attacks on Obama's past links to 1960s radical Bill Ayers and lambasted his opponent's credentials to be commander-in-chief.

"I think this whole issue of the relationship with Bill Ayers needs to be known by the American people," the Arizona senator told Spanish-language station Radio Mambi.

"Senator Obama said it was just a guy in the neighbourhood. We know much more than that."

Ayers was a member of the "Weathermen" movement which carried out a series of bombings to protest the Vietnam War, including on the Pentagon and US Capitol. Obama's campaign say he has had no contact with Ayers since 2005.

McCain has desisted from mentioning Ayers in recent speeches, but his comments could signal a fresh onslaught on Obama's character as the election campaign enters the finishing stretch.

Later on Wednesday McCain painted a doom-laden picture of what may happen to the United States if Obama is elected, saying his rival would oversee defeat in Iraq and was incapable of protecting Americans from terrorism.

"With terrorists still plotting new strikes across the world, millions of innocent lives are still at stake, including American lives," he said.

"The question is whether this is a man who has what it takes to protect America from Osama bin Laden, al-Qaeda, and other grave threats in the world," McCain said. "And he has given you no reason to answer in the affirmative."

Economy more important

Whether McCain's tactics are successful remain to be seen. Polls have repeatedly shown that the economy rather than national security remains the defining issue of the campaign.

A new poll from Quinnipiac University on Wednesday showed Obama with a still sizeable, albeit slightly narrower lead in Ohio and Pennsylvania but with Florida now too close to call.

Another poll from Rasmussen Reports meanwhile showed McCain closing to within three points of Obama nationwide for the first time in more than month, trailing 47 percent to 50 percent.

But a survey of battleground states by CNN and Time had Obama expanding his lead in Colorado and holding steady margins in Florida and Virginia.

Republican vice presidential candidate Sarah Palin hinted in an interview with ABC News to be broadcast on Thursday that she will remain a key player in US politics regardless of who gets elected president next week, and may even run in the 2012 election.

A transcript of the interview was made public late on Wednesday.

"I'm not doing this for naught," Palin said, when asked if all the mudslinging in the current campaign made her long for a return to the politics of Alaska, where she is governor.

AFP