The mistake, which he quickly corrected after a whisper from a colleague, was an unwelcome stumble as the Arizona senator, the all-but-certain Republican presidential nominee, spends seven days in the Mideast and Europe.

His campaign asserts that McCain's decades of foreign-policy experience make him the candidate best equipped to lead the country in a time of international peril. He has staked his bid in particular on his deep knowledge of the military and political situation in Iraq, frequently mocking his Democratic rivals for what he describes as a naive desire to pull troops out quickly.

McCain is spending two days in Israel after 48 hours in Iraq, where he met with top Iraqi officials and U.S. military officers to assess progress.

Standing with fellow Sens. Joseph Lieberman (I., Conn.) and Lindsey Graham (R., S.C.) at the Citadel, a set of ancient ruins in Amman, McCain said he was concerned about Iran's influence in Iraq and cited a recently discovered cache of weapons that he said could be particularly lethal in being used to target Americans in the country.

"We continue to be concerned about Iranian [operatives] taking al-Qaeda into Iran, training them and sending them back," he said in comments after meeting with Jordan's King Abdullah II.

Pressed to elaborate, McCain said it was "common knowledge and has been reported in the media that al-Qaeda is going back into Iran and receiving training and are coming back into Iraq from Iran . . . and it's unfortunate."

A few moments later, Lieberman whispered in his ear. McCain then said: "I'm sorry, the Iranians are training extremists, not al-Qaeda."

The United States has long asserted that elements of Iran's security forces have been training and supplying weapons to Iraq's Shiite militias. Iran is an overwhelmingly Shiite country whose government has applauded the emergence of a Shiite-led government in Iraq but has denied supporting Shiite militias.

Al-Qaeda in Iraq is a predominantly Sunni group blamed for deadly mass killings of Shiites and attacks on U.S. forces. Some Sunni extremists consider Shiites to be heretics and therefore legitimate targets of attack. The schism between Islam's Sunni and Shiite sects grew out of a dispute over the leadership of the faithful after the death of the prophet Muhammad in 632.

Democrats pointed out that McCain made the same assertion in a radio interview Monday with talk-show host Hugh Hewitt, saying: "There are al-Qaeda operatives that are taken back into Iran, given training as leaders, and they're moving back into Iraq."

In a statement, Democratic Party spokeswoman Karen Finney seized on the mistakes. Not only is McCain "wrong on Iraq once again," she said, "but he showed he either doesn't understand the challenges facing Iraq and the region or is willing to ignore the facts on the ground."

Brian Rogers, a spokesman for McCain's campaign, accused the Democrats of unwarranted political attacks.

Rogers said from McCain's Virginia headquarters that the senator "misspoke and immediately corrected himself by stating that Iran is in fact supporting radical Islamic extremists in Iraq, not al-Qaeda - as the transcript shows."

McCain has said he is leading the three-person delegation abroad as a member of the Senate Armed Services Committee, not as a candidate for president. But he is giving daily interviews to U.S. networks and will hold a fund-raiser in London tomorrow.

His political advisers had said a side benefit from the trip would be images of McCain standing shoulder-to-shoulder with world leaders and showing his expertise on issues of war, foreign policy and terrorism. McCain continued that effort after leaving Jordan, meeting Israeli President Shimon Peres in Jerusalem before other high-level talks in the city today.