BOCA RATON, Florida (AFP) — US President Barack Obama and his Republican challenger Mitt Romney on Monday face off in their third and final debate, with polls showing them dead even in their race for the White House.

The showdown focusing on foreign policy is being held in the critical toss-up state of Florida just 15 days before the election and promises to be among the most watched 90 minutes of the entire 2012 campaign.

Upping the stakes, a new NBC/Wall Street Journal poll released on the eve of the duel showed the rivals in a dead heat, with 47 per cent each among likely voters.

“This debate will be a big one,” said Dan Gelber, a former state senator from Miami Beach who is working with the Obama campaign. “We have a lot of communities here that care about foreign policy, especially in South Florida, whether it’s the Jewish community, the Cuban community, the Haitian community or the Hispanic community across the state.”

The president and his Republican rival will no doubt trade blows over security shortcomings in Libya; how to contain Iran; the roiling crisis in Syria; a rising China; and ending the Afghan war.

It will be Romney’s best chance to recover from what are seen as mis-steps in criticising Obama’s handling of the September 11 attack on the US consulate in Benghazi, Libya that left four Americans dead.

Romney will be aiming to use the head-to-head clash to press his broader point that the Libya attack and other anti-American violence in the Middle East are signs that Obama’s foreign policy is “unraveling before our very eyes.”

Romney is a former businessman who appears more comfortable addressing economic problems. He has stumbled at times on international issues, and his foreign tour last summer was widely panned.

But Obama too has issues; a Pew Research Center poll shows his advantage on foreign policy shrinking to just four points over Romney, after being up 15 points last month.

Obama’s mission: remind Americans of his successes as commander-in-chief, such as ending the Iraq war and neutralising Osama bin Laden, while convincing them that his rival is a throwback to the George W Bush era who doesn’t have the experience or resolve to steer the nation through a crisis.

With Romney dominating the first face-to-face encounter in Colorado, and Obama widely seen as bouncing back to take the second outside New York city, the stakes for round three are monumental.

Even with the zeroing in on international affairs, both camps admitted Sunday that their candidates will seek to draw discussion back to the issue most pressing for voters: the US economy.

“I think the most important thing we can do as a country on our foreign policy is strengthen our economy here at home,” Chicago Mayor Rahm Emanuel, Obama’s former chief of staff, said Sunday.

Romney has spoken repeatedly about how a strong domestic economy projects US strength and leadership abroad.

He and Obama will will face questions about crises like Libya, which has remained a front-burner issue some six weeks after the September 11 attack.

Many analysts said Obama bested Romney on the Libya issue in their testy second debate, when Romney accused the president of delaying a full two weeks before describing the Benghazi attack as terrorism.

Obama shot back that he called it an act of terror on the day after the attack, challenging Romney to “check the transcript” and berating him for trying to make political gains after the attack.

Romney will seek to put pressure on Obama over Iran and its nuclear programme, arguing that presidential weakness has emboldened Tehran, and that if elected he would work to prevent the Islamic republic from acquiring a nuclear weapons “capability,” a lower threshold than advocated by the White House.

Complicating the scenario, just 48 hours before the debate, The New York Times reported that US officials said Iran was ready to hold one-on-one talks with Washington.

The White House shot down the story, but Republican surrogates used it to warn Obama about potentially isolating allies who have worked for years on getting Iran to halt its nuclear programme.