Estimates of the size of the insurgency vary. A senior military officer who works the issue and who last autumn put the number of "committed fighters" at 5,000 -- a figure disclosed publicly in November by Gen. John P. Abizaid, the top U.S. commander in the Persian Gulf region -- said that he now estimates they have grown to as many as 12,000.
He said the insurgency has expanded in part because of mounting Iraqi irritation with the presence of U.S. troops in Iraq. Other contributing factors, he said, include the scandal over mistreatment of prisoners at U.S.-run detention centers and the rise of Sadr's militia.
The strategy to differentiate between extremist elements who are considered lost causes and those in the Sunni resistance who might be persuaded to drop their opposition was formalized in Pentagon planning documents in August and has been refined several times since, defense officials said. Alluding to the plan, Defense Secretary Donald H. Rumsfeld has spoken in recent weeks of methodical attempts by U.S. and Iraqi authorities to reach political accords with resistance groups. Iraq's interim prime minister, Ayad Allawi, who took office in June, also has made clear his desire to extend an olive branch to some Sunni militants.
In cases where these diplomatic efforts fail, Rumsfeld has signaled the likely use of military force, as was demonstrated four weeks ago in Samarra. Pentagon officials said the most critical test will come in an increasingly likely assault on more than 3,000 insurgents in Fallujah and Ramadi.
Over the past year, the U.S. view of the insurgency has evolved. Rumsfeld initially spoke dismissively of enemy fighters in Iraq as "dead-enders" -- referring to remnants of Hussein's Baath party, elements of his Special Republican Guard and other specialized units. As attacks continued, many were blamed on al Qaeda and affiliates such as Ansar al-Islam and other foreign fighters said to be entering from Syria.
More recently, senior officials have described an expanded and deeply entrenched array of Sunni cells in particular. They have cited evidence of plans by Hussein's closest advisers before the U.S. invasion to regroup in small cells afterward. They also say some former Baathist officials dispersed after the war began and began providing financing from outside as well as inside Iraq.
One senior defense official said more than a dozen "financial people" from Hussein's government have been identified funneling money from Syria to insurgents in Iraq. Izzat Ibrahim Douri, a former senior Baath Party official, is among those said to have traveled to Syria to help set up a support network. He is now believed to be back in Iraq and playing a significant role in coordinating attacks.
"The real enemy are the FRE," said the senior military officer, using the abbreviation for former regime elements. "But the problem with the FRE is they're so ingrained, so insidiously situated within Iraqi society."
Citing their ruthless violence and brutal intimidation, he likened them to the New York mafia in the 1930s, "where they owned blocks, where people wouldn't tell on them because they knew they'd have their throat slit." He called them "a very difficult target."
The view of Iraq's insurgency as a disparate assortment of groups is supported by a number of experts outside the U.S. government. While they describe the insurgency as lacking unity or a long-term vision, they also say it seems not to have suffered as a result.
"The insurgents may have calculated that their success does not now require an elaborate political and socioeconomic vision of a 'free' Iraq," said Ahmed S. Hashim, professor of strategic studies at the Naval War College and a consultant to Abizaid's Central Command. "Articulating the desire to be free of foreign occupation has sufficed to win popular support."
"The insurgents represent different philosophies but they all want to get us out of Iraq," said Bodine, the former State Department official. "There is no clear national leadership and no politics -- at least not yet -- but we're not far from a time when it could become national."
W. Patrick Lang, a former Army colonel and Middle East specialist in the Defense Intelligence Agency, said the insurgents were pursuing "a strategy of isolation of the occupier."
