BOCA RATON, Fla. - President Barack Obama and Republican challenger Mitt Romney clashed over US military strength and how to deal with crises in the Middle East in a third and final debate on Monday as polls showed them in deadlock two weeks before the Nov. 6 election.

US Republican presidential nominee Mitt Romney (L) answers a question as US President Barack Obama listens during the final US presidential debate in Boca Raton, Florida, Oct 22, 2012. [Photo/Agencies]

With one last chance for both men to appeal to millions of voters watching on television, Obama was the aggressor from the start. He criticized the Republican on his proposals on the Middle East, mocking his calls for more ships in the US military and saying Romney wants to bring the United States back to a long-abandoned Cold War stance.

Obama had a biting response when Romney said he would increase the number of ships built by the US Navy, saying the United States should typically have 300 and only had 285.

"Governor, we also have fewer horses and bayonets," said Obama.

Obama also said the Republican presidential candidate, by once declaring Russia a "geopolitical foe" of the United States, was seeking to turn back the clock.

"The Cold War has been over for 20 years," Obama said, turning to Romney as they sat at a table before moderator Bob Schieffer. "When it comes to your foreign policy, you seem to want to import the foreign policies of the 1980s."

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Romney, wanting to make no mistakes that could blunt his recent surge in the polls, said Obama's policies toward the Middle East and North Africa were not stopping a resurgence of the threat from al Qaeda in the region.

"Attacking me is not an agenda," said Romney. "Attacking me is not how we deal with the challenges of the Middle East."

The two candidates agreed that the United States should defend Israel if Iran attacked the key US ally in the Middle East, but Romney said he would tighten sanctions that are already affecting the Iranian economy.

The Republican, whose central theme throughout the campaign has been a promise to rebuild the weak US economy, repeatedly turned the discussion back to economic matters, saying US national security depended on a strong economy.

But Obama fired back that Romney's economic plan was based on tax cuts that had not had their desired effect in the past. Romney would not be able to balance the budget and increase military spending with such a plan, he said.

"The math simply does not add up," he said.

'BACKBONE' ON RUSSIA

On Russia, Romney criticized Obama for an open-microphone comment he made to then-Russian President Dmitry Medvedev that he would have more "flexibility" after America's election.

Instead of showing Russian President Vladimir Putin more flexibility, Romney said, "I'll give him more backbone."

The two candidates were tied at 46 percent each in the Reuters/Ipsos online daily tracking poll. Other surveys show a similar picture.

Obama came to Boca Raton with the advantage of having led US national security and foreign affairs for the past 3 1/2 years. He gets credit for ending the Iraq war and the killing of al Qaeda leader Osama bin Laden in 2011.

But Romney had many opportunities to steer the conversation back toward the weak US economy, a topic on which voters see him as more credible.

Quotes from last US presidential debate

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