But other estimates suggest the sums involved could be far higher. The oil ministry in Baghdad, for example, estimated earlier this year that 10 percent to 30 percent of the $4 billion to $5 billion in fuel imported for public consumption in 2005 was smuggled back out of the country for resale. At that time, the finance minister estimated that close to half of all smuggling profits was going to insurgents. If true, that would be $200 million or more from fuel smuggling alone.

For Washington, the report’s most dismaying finding may be that the insurgency now survives off money generated from activities inside Iraq, and no longer depends on sums Mr. Hussein and his associates seized as his government collapsed. American officials said that as American troops entered Baghdad, Mr. Hussein’s oldest son, Qusay, took more than $1 billion in cash from the Central Bank of Iraq and stashed it in steel trunks aboard a flatbed truck. Large sums of cash were found in Mr. Hussein’s briefcase when he was captured in December 2003.

But the report says Mr. Hussein’s loyalists “are no longer a major source of funding for terrorist or insurgent groups in Iraq.” Part of the reason, the report says, is that an American-led international effort has frozen $3.6 billion in “former regime assets.” Another reason, it says, is that Mr. Hussein’s erstwhile loyalists, realizing that “it is increasingly obvious that a Baathist regime will not regain power in Iraq,” have turned increasingly to spending the money on their own living expenses. The trail to these assets “has grown cold,” the report adds.

The document says the pattern of insurgent financing changed after the first 18 months of the war, from the Hussein loyalists who financed it in 2003 to “foreign fighters and couriers” smuggling cash in bulk across Iraq’s porous borders in 2004, to the present reliance on a complex array of indigenous sources. “Currently, we assess that these groups garner most of their funding from petroleum-related criminal activity, kidnapping and other criminal pursuits within Iraq,” the report concludes.

Image Suspected insurgents fighting on the streets of Ramadi in a 2005 photo. An American study offers little hope that much can be done to choke off revenues to the armed groups battling the government in Iraq. Credit... Bilal Hussein/Associated Press

One section of the report is dedicated to the role played by “sympathetic donors,” including Islamic charities and nongovernmental organizations. It says that “intelligence reporting” indicates that only 10 to 15 of the 4,000 nongovernmental groups support terrorist and insurgent groups, but that those few take advantage of lax Iraqi regulation to divert funds to insurgent and other armed groups and, in some cases, “to provide cover for insurgent recruitment and the transport of weapons and personnel.”

The possibility that Iraq-based terrorist groups could finance attacks outside Iraq appeared to echo Bush administration assertions that prevailing in the war here is essential to preventing Iraq from becoming a terrorist haven, as Afghanistan became under the Taliban. But that suggestion was one of several aspects of the report that drew criticism from Western terrorism and counterinsurgency experts working outside the government who were given the outline of the findings.