US President Barack Obama and his Republican challenger Mitt Romney on Monday face off in their third and final debate, with latest 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 percent 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 criticizing Obama's handling of the 9/11 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 neutralizing Osama bin Laden, while convincing them that his rival is a throwback to the George W. Bush administration, which doesn't have the experience or resolve to steer the country through a crisis.

Romney and Obama will will face questions about crises like Libya, which has remained a front-burner issue some six weeks after the 9/11 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.