BAGHDAD - In rebuffing calls to bring troops home from Iraq, President Bush on Thursday employed a stark and ominous defense. "The same folks that are bombing innocent people in Iraq," he said, "were the ones who attacked us in America on September the 11th, and that's why what happens in Iraq matters to the security here at home."
It is an argument Mr. Bush has been making with frequency in the past few months, as the challenges to the continuation of the war have grown. On Thursday alone, he referred at least 30 times to Al Qaeda or its presence in Iraq.
But his references to Al Qaeda in Mesopotamia, and his assertions that it is the same group that attacked the United States in 2001, have greatly oversimplified the nature of the insurgency in Iraq and its relationship with the Qaeda leadership.
There is no question that the group is one of the most dangerous in Iraq. But Mr. Bush's critics argue that he has overstated the Qaeda connection in an attempt to exploit the same kinds of post-Sept. 11 emotions that helped him win support for the invasion in the first place.
Al Qaeda in Mesopotamia did not exist before the Sept. 11 attacks. The Sunni group thrived as a magnet for recruiting and a force for violence largely because of the American invasion of Iraq in 2003, which brought an American occupying force of more than 100,000 troops to the heart of the Middle East, and led to a Shiite-dominated government in Baghdad.
The American military and American intelligence agencies characterize Al Qaeda in Mesopotamia as a ruthless, mostly foreign-led group that is responsible for a disproportionately large share of the suicide car bomb attacks that have stoked sectarian violence. Gen. David H. Petraeus, the senior American commander in Iraq, said in an interview that he considered the group to be "the principal short-term threat to Iraq."
But while American intelligence agencies have pointed to links between leaders of Al Qaeda in Mesopotamia and the top leadership of the broader Qaeda group, the militant group is in many respects an Iraqi phenomenon. They believe the membership of the group is overwhelmingly Iraqi. Its financing is derived largely indigenously from kidnappings and other criminal activities. And many of its most ardent foes are close at home, namely the Shiite militias and the Iranians who are deemed to support them.
"The president wants to play on Al Qaeda because he thinks Americans understand the threat Al Qaeda poses," said Bruce Riedel, an expert at the Saban Center for Middle East Policy and a former C.I.A. official. "But I don't think he demonstrates that fighting Al Qaeda in Iraq precludes Al Qaeda from attacking America here tomorrow. Al Qaeda, both in Iraq and globally, thrives on the American occupation."
Abu Musab al-Zarqawi, a Jordanian who became the leader of Al Qaeda in Mesopotamia, came to Iraq in 2002 when Saddam Hussein was still in power, but there is no evidence that Mr. Hussein's government provided support for Mr. Zarqawi and his followers. Mr. Zarqawi did have support from senior Qaeda leaders, American intelligence agencies believe, and his organization grew in the chaos of post-Hussein Iraq.
"There has been an intimate relationship between them from the beginning," Mr. Riedel said of Al Qaeda in Mesopotamia and the senior leaders of the broader Qaeda group.
But the precise relationship between the Al Qaeda of Osama bin Laden and other groups that claim inspiration or affiliation with it is murky and opaque. While the groups share a common ideology, the Iraq-based group has enjoyed considerable autonomy. Ayman al-Zawahri, Osama bin Laden's top deputy, questioned Mr. Zarqawi's strategy of organizing attacks against Shiites, according to captured materials. But Mr. Zarqawi clung to his strategy of mounting sectarian attacks in an effort to foment a civil war and make the American occupation untenable.
The precise size of Al Qaeda in Mesopotamia is not known. Estimates are that it may have from a few thousand to 5,000 fighters and perhaps twice as many supporters. While the membership of the group is mostly Iraqi, the role that foreigners play is crucial.
Abu Ayyub al-Masri is an Egyptian militant who emerged as the successor of Mr. Zarqawi, who was killed near Baquba in an American airstrike last year. American military officials say that 60 to 80 foreign fighters come to Iraq each month to fight for the group, and that 80 to 90 percent of suicide attacks in Iraq have been conducted by foreign-born operatives of Al Qaeda in Mesopotamia.
At first, Al Qaeda in Mesopotamia received financing from the broader Qaeda organization, American intelligence agencies have concluded. Now, however, the Iraq-based group sustains itself through kidnapping, smuggling and criminal activities and some foreign contributions.
With the Shiite militias having taken a lower profile since the troop increase began, and with Al Qaeda in Mesopotamia embarking on its own sort of countersurge, a main focus of the American military operation is to deprive the group of its strongholds in the areas surrounding Baghdad - and thus curtail its ability to carry out spectacular casualty-inducing attacks in the Iraqi capital.
The heated debate over Iraq has spilled over to Al Qaeda in Mesopotamia as well. Mr. Bush has played up the group, talking about it as if it is on a par with the perpetrators of the Sept. 11 attacks. War critics have often played down the significance of the group despite its gruesome record of suicide attacks and its widely suspected role in destroying a Shiite shrine in Samarra in February 2006 that set Iraq on the road to civil war.
Just last week, Mr. Zawahri called on Muslims to travel to Iraq, Afghanistan and Somalia to carry out their fight against the Americans and appealed for Muslims to support the Islamic State in Iraq, an umbrella group that Al Qaeda in Mesopotamia has established to attract broader Sunni support.
The broader issue is whether Iraq is a central front in the war against Al Qaeda, as Mr. Bush maintains, or a distraction that has diverted the United States from focusing on the Qaeda sanctuaries in Pakistan while providing Qaeda leaders with a cause for rallying support.
Military intelligence officials said that Al Qaeda in Mesopotamia's leaders wanted to expand their attacks to other countries. They noted that Mr. Zarqawi claimed a role in a 2005 terrorist attack in Jordan. But Bruce Hoffman, a terrorism expert at Georgetown University, said that if American forces were to withdraw from Iraq, the vast majority of the group's members would likely be more focused on battling Shiite militias in the struggle for dominance in Iraq than on trying to follow the Americans home.
"Al-Masri may have more grandiose expectations, but that does not mean he could turn Al Qaeda of Iraq into a transnational terrorist entity," he said.
Michael R. Gordon reported from Baghdad, and Jim Rutenberg from Washington.
Copyright 2007 The New York Times Company