WASHINGTON, Feb. 20 — The most active terrorist network inside Iraq appears to be operating mostly apart from Al Qaeda, senior American officials say.
Most significantly, the officials said, American intelligence had picked up signs that Qaeda members outside Iraq had refused a request from the group, Ansar al-Islam, for help in attacking Shiite Muslims in Iraq.
The request was made by Ansar's leader, a Jordanian, Abu Musab al-Zarqawi, and intercepted by the United States last month. The apparent refusal is being described by some American intelligence analysts as an indication of a significant divide between the groups.
Since before the American invasion, Bush administration officials have portrayed Al Qaeda and Ansar as close associates and used the links as part of their justification for war against Saddam Hussein's government.
The officials declined this week to say how American intelligence agencies had learned that members of Al Qaeda had rebuffed Mr. Zarqawi's proposal. One of his top lieutenants, Hassan Ghul, has been in American custody for several weeks.
In an interview today, one official cautioned that it would be a mistake to see the two groups as having diverged, and that it was too soon to say whether Al Qaeda might support Mr. Zarqawi. This official described the fact that Mr. Zarqawi had appealed for help as a sign of "emerging links" between the two groups.
"Maybe someone did say no, but that doesn't mean they'll say no tomorrow," the official said.
But, officials said, there are growing indications that the two groups are distinct and independent, and are embracing different tactics and agendas.
A recent report by the State Department's intelligence branch emphasizes those differences, according to American officials who have read the classified document.
"Even among Sunni Muslim extremists and committed terrorists, including Zarqawi and Al Qaeda, there can be extreme discrepancies about strategy and tactics," one senior official said. "This is not a world of homogeneous bad guys."
Even if Mr. Zarqawi and Ansar are not working closely with Al Qaeda, they appear to be getting logistical support from outside Iraq, the American officials said.
A recent report by one intelligence agency shows lines of support, including supplies, money and recruiting, that extend to Mr. Zarqawi's group from neighboring countries, including Iran, Turkey, Syria and Saudi Arabia.
Mr. Zarqawi himself has traveled in and out of Iraq from Iran, where he took refuge after the American invasion last March, and from Syria, two military officials said.
In public reports and private statements, American intelligence officials have been careful to portray Mr. Zarqawi as an associate of Al Qaeda rather than as a member.
But before the American invasion, Bush administration officials portrayed Mr. Zarqawi's presence in Iraq, which they said required the support of Mr. Hussein's government, as their best evidence of links between Iraq and Al Qaeda.
"Iraq today harbors a deadly terrorist network headed by Abu Musab al-Zarqawi, an associate and collaborator of Osama bin Laden and his Al Qaeda lieutenants," Secretary of State Colin L. Powell told the United Nations Security Council last February.
American intelligence officials continue to describe Ansar, which has many foreign members, as the most dangerous terrorist network operating in Iraq.
By contrast, the evidence since the war began of operations inside Iraq by Al Qaeda has been limited and generally inconclusive, American officials say. American intelligence officers believe Qaeda leaders to be in Afghanistan and Pakistan.
The intercepted letter from Mr. Zarqawi to Al Qaeda leaders was made public last week by American officials after its contents were first reported by The New York Times.
In a version translated into English by American military officials, Mr. Zarqawi appears to anticipate that his idea of attacking Shiite Muslims might stir opposition from Al Qaeda, which has generally avoided direct strikes on fellow Muslims. The tactic is intended to ignite sectarian clashes inside Iraq and, ultimately, indirectly enlist more Iraqi Sunnis in a campaign aimed at ousting American forces.
"Some people will say that this will be a reckless and irresponsible action that will bring the Islamic nation to a battle for which the Islamic nation is unprepared," the letter said. "Souls will perish and blood will be spilled. This is, however, exactly what we want."