By DAVID ESPO and KASIE HUNT

Associated Press

BOCA RATON, Fla.

--President Barack Obama sharply challenged Mitt Romney on foreign policy in their final campaign debate Monday night, saying, "Every time you've offered an opinion you've been wrong." The Republican coolly responded, "Attacking me is not an agenda" for dealing with a dangerous world.

Romney took the offensive, too. When Obama said the U.S. and its allies have imposed crippling sanctions on Iran to halt nuclear weapons development, the Republican challenger responded that the U.S. should have done more. He declared repeatedly, "We're four years closer to a nuclear Iran."

Despite the debate's foreign affairs focus, the rivals turned the discussion back to the slowly recovering U.S. economy, which polls show is the No. 1 issue for most voters.

They found little agreement on that, but each stressed unequivocal support for Israel when asked how he would respond if the Jewish state were attacked by Iran.

"If Israel is attacked, we have their back," said Romney--moments after Obama vowed, "I will stand with Israel if Israel is attacked."

Both also said they oppose direct U.S. military involvement in the efforts to topple Syrian President Bashir Assad.

The debate produced none of the theatrics seen at last week's face-off. But the two men frequently sniped at each other even on issues where they agree, and reprised their campaign-long disagreements over the economy, energy, education and other domestic issues.

Obama and Romney are locked in a close race in national opinion polls. The final debate behind them, both men intend to embark on a final two-week whirlwind of campaigning.

On the Middle East, Romney said that despite early hopes, the ouster of despotic regimes in Egypt, Libya and elsewhere over the past year has resulted in a "rising tide of chaos." He said the president has failed to come up with a coherent policy to grapple with change sweeping the Middle East, and he added ominously that an al-Qaida-like group has taken over northern Mali.

Anticipating one of Obama's most frequent campaign assertions, Romney said of the man seated nearby, "I congratulate him on taking out Osama bin Laden and taking on the leadership of al-Qaida. But we can't kill our way out of this. We must have a comprehensive strategy."