Iraq's armed guerillas are usually portrayed in vague and shadowy terms, allowing political commentators to cast them in whatever image is deemed convenient. Even the correct word to designate them says more about the commentator than the militants themselves. Those who wish to demonize them call them "terrorists"; those who wish to cheer them on call them the "resistance"; while the majority of the mainstream media cut it down the middle by calling them "insurgents"—while still providing little detail about who they actually are.

Now a front-page Dec. 2 New York Times story (online at the International Herald Tribune) actually provides a breakdown of the insurgency's major constituent entities, and an analysis of its strategies and structure, drawing on the research of the SITE Institute (for Seach for International Terrorist Entities).

The SITE Institute identifies five major groupings, each made up of numerous small, largely autonomous cells that operate under its umbrella. From largest to smallest: al-Qaeda in Mesopotamia, Ansar al-Sunna, the Victorious Army Group, the 20th of July Revolution Brigade and al-Rashideen Army.

The report recognizes this decentralized structure as one of the movement's strengths:

Highly visible groups like Al Qaeda, Ansar al Sunna and the Victorious Army Group appear to act as fronts, the Iraqis and the Americans say, providing money, general direction and expertise to the smaller groups, but often taking responsibility for their attacks by broadcasting them across the globe.

"The leaders usually don't have anything to do with details," said Abdul Kareem al-Eniezi, the Iraqi minister for national security. "Sometimes they will give the smaller groups a target, or a type of target. The groups aren't connected to each other. They are not that organized."

Some experts and officials say there are important exceptions: that Al Qaeda's leaders, for instance, are deeply involved in spectacular suicide bombings, the majority of which are still believed to be carried out by foreigners. They also say some of the smaller groups that claim responsibility for attacks may be largely fictional, made up of ragtag groups of fighters hoping to make themselves seem more formidable and numerous than they really are.

But whatever the appearances, American and Iraqi officials agree on the essential structure of the Iraqi insurgency: it is horizontal as opposed to hierarchical, and ad hoc as opposed to unified. They say this central characteristic, similar to that of terrorist organizations in Europe and Asia, is what is making the Iraqi insurgency so difficult to destroy. Attack any single part of it, and the rest carries on largely untouched. It cannot be decapitated, because the insurgency, for the most part, has no head. Only recently, American and Iraqi experts say, have they begun to grasp the new organizational structure that, among other things, is making the insurgency so difficult to stop.

Thus, even the death or capture of Iraq's presumed al-Qaeda leader Abu Musab al-Zarqawi wouldn't necessarily make much difference.

There is no center of gravity, no leadership, no hierarchy; they are more a constellation than an organization," said Bruce Hoffman, a terrorism expert at the Rand Corporation. "They have adopted a structure that assures their longevity."

The insurgency's survivability presents perhaps the most difficult long-term challenge for the Iraqi government and American commanders. The primary military goal of groups like Al Qaeda and Ansar al Sunna is not to win but simply not to lose; to hang on until the United States runs out of will and departs. Even killing or capturing the leader of Al Qaeda in Mesopotamia, Abu Musab al-Zarqawi, many Iraqi and American officials say, will not end the rebellion.

In a war as murky as the one in Iraq, details about the workings of the insurgency are fleeting and few. But what is available suggests that the movement is often atomized and fragmented, but no less lethal for being so. A review of the dozens of proclamations made by jihadi groups and posted on Islamist Web sites found more than 100 different groups that either claimed to be operating in Iraq or were being claimed by an umbrella group like Al Qaeda.

Most of the Internet postings were located and translated by the SITE Institute, the Washington group that, among other things, tracks insurgent activity on the Web.

Of the groups found by SITE, 59 were claimed by Al Qaeda and 36 by Ansar al Sunna. Eight groups claimed to be operating under the direction of the Victorious Army Group, and five groups said they were operating under the 20th of July Revolution Brigade.

The complex nature of the insurgency was illustrated on Oct. 24, when three suicide bombers, one driving a cement mixer full of TNT, staged a coordinated attack on the Palestine and Sheraton Hotels in central Baghdad. The attack was one of the most sophisticated yet, with the first explosion ripping open a breach in the hotels' barriers. That allowed the cement mixer to come within a few yards of the Sheraton before being hung up in barbed wire.

An American solider opened fire on the driver of the truck, and the bomb was apparently detonated by remote control. Twelve people died, and American and Iraqis agreed later that the attack had come very close to bringing both towers down.

Within 24 hours, Al Qaeda, in an Internet posting viewed round the world, boasted of its role in attacking the "crusaders and their midgets."

But in the small print of the group's proclamation, Al Qaeda declared that the attack had actually been carried out by three separate groups: the Attack Brigade, the Rockets Brigade and Al Baraa bin Malik Suicide Brigade. The three groups, the Qaeda notice said, had acted in "collaboration," with some fighters conducting surveillance while others provided cover fire.

Rita Katz, the director of SITE, which is now working under a United States government contract to investigate militant groups, said the attack on the Palestine and Sheraton Hotels had probably been planned and directed at the highest levels of Al Qaeda.

The leaders may have brought the three "brigades" together to stage the attack, she said, and probably provided expertise as well as the suicide bombers themselves.

The report actually notes differences in tactics and ideology among the insurgent groups.

American and Iraqi experts also say there appear to be important distinctions among the umbrella groups. While Islamist groups like Al Qaeda and Ansar al Sunna attack military and civilian targets at will, other organizations, like the Victorious Army Group, which is believed to be associated with followers of Saddam Hussein's government, appear to attack only American or Iraqi solders.

In recent months, some insurgent groups have refined their target goals even further. In July, Al Qaeda said it had formed a group called the Omar Brigade to focus on killing members of Shiite militias like the Badr Brigade. Since then, the Omar Brigade has taken responsibility for dozens of killings.

Some insurgent groups appear to be limited to exclusive geographic areas. The Zi al Nourein Brigade, whose exploits are regularly proclaimed by Ansar al Sunna, appears to operate almost exclusively in Mosul, in northern Iraq. Each week, more such groups announce their presence.

"Following Allah's orders to his worshipers, the mujahedeen, to join together and stand in one line against Allah's enemies," a posting on the Internet said July 12, "Al Miqaeda Brigade Groups announced that they are joining Ansar al Sunna.

And, of course, factionalism:

The array of insurgent groups has prompted competition among them. On the streets of Ramadi, the violent city west of Baghdad, a leaflet found on the street, signed by a group called the Islamic Army, said that "the growing number of mujahedeen groups, which grew in number when the people realized their value," had caused confusion about which group was speaking for which.

The Islamic Army leaflet read like an advertisement offered by a product manager worried about imitators.

"We are asking people to reject any statement signed by the Sajeel Battalion of the Islamic Army that does not carry their slogan or seal," the leaflet said.

One question that remains unsettled is the nationalities of suicide bombers. American and Iraqi officials have long said they believe that the majority of suicide attacks are carried out by foreigners.

In June, in an apparent answer to that question, Al Qaeda announced the formation of the Ansar Brigade, which it described as an all-Iraqi suicide unit. Since then, the Ansar Brigade has taken responsibility for few such attacks.

One place where the Ansar Brigade did apparently strike was Jordan last month, when suicide bombers struck three hotels in Amman. The police there determined that Iraqis had carried out the attack.

In a message posted on the Internet, Al Qaeda announced that the Ansar Brigade, its Iraqi suicide group, had carried out the attack.

This enlightening report indicates that those in the establishment who have sought to demonize the insurgents as "terrorists" who can be neatly decapitated and defeated are finally beginning to wake up to the complexities of the situation. Can we say likewise of the more kneejerk among those in the anti-war camp who have sought to glorify the insurgents as the "resistance"—or else idiotically claimed that all attacks on civilians have really been the work of Pentagon "black ops"?

See our last post on Iraq and the armed resistance.