HADITHA, Iraq — In the region around Qaim, a northwestern Iraqi town near the Syrian border, Marines are fanning out from their main base and moving into villages as part of a new strategy to root out insurgents who enter the country here.
The troops have set up 19 small base camps throughout the area and begun routinely patrolling insurgent hot spots north of the Euphrates River. The deployment follows a strategy favored by a new generation of counterinsurgency experts: disperse, mingle with the population and stay put.
But the shift comes as the Pentagon appears to be moving the overall U.S. military effort in the opposite direction across much of the country. Army units are being concentrated in "super bases" that line the spine of central Iraq, away from the urban centers where counterinsurgency operations take place.
The two approaches underscore an increasingly high-profile divergence -- some say contradiction -- on how best to use U.S. forces in Iraq, and are evidence of a growing debate in the upper ranks about the wisest course of action.
The contrast also reflects the complicated mix of military goals and concerns as U.S. troops begin their fourth summer in Iraq. Top commanders are eager to begin shrinking the U.S. footprint, an implicit step toward a gradual withdrawal of American forces. At the same time, some field commanders are determined to break an endless cycle that allows insurgents to move back into key areas as soon as U.S. forces move on. That requires large investments of manpower.
Some military officials insist that the two strategies can coexist, particularly given that Iraqis are being trained in counterinsurgency and are expected to assume a larger role, with help from American advisors. But critics consider it a choice between a smaller force and an effective one.
On one side of the strategy debate is a growing cadre of military intellectuals and counterinsurgency experts who advocate an on-the-ground effort to deal with the insurgency, military analysts say. This group includes, along with Marine units such as those in western Iraq, mid-level officers such as Col. H.R. McMaster, commander of Army forces in Tall Afar, where a counterinsurgency campaign has been cited by President Bush as a model for the country.
On the other side are senior officers, including those at the U.S. Central Command, who believe a reduced American presence will force Iraqis to take up the burden of fighting the insurgency. Some have also argued that a high-profile U.S. presence in cities stokes resentment.
The debate mirrors a discussion over the general posture of U.S. troops in Iraq. Lt. Gen. Peter Chiarelli, in charge of day-to-day military operations, said in an interview with The Times this week that "heavy-handed" treatment of Iraqis by U.S. forces fueled anti-American attitudes.
In the counterinsurgency debate, experts both inside and outside the Pentagon have begun to question the move to big bases and the push to reduce troop numbers, particularly when Iraqi forces -- especially the Iraqi police, which have in some cases been accused of being branches of sectarian militia -- have yet to prove themselves.
"What we know works is presence; that was most visible in Tall Afar," said Kalev Sepp, an instructor at the Naval Postgraduate School who helped write a critique of counterinsurgency strategy for Army Gen. George W. Casey, the top U.S. commander in Iraq.
"The key to counterinsurgency is presence among the population," Sepp said. "What do mass concentrations of American forces on a large base do? If we put all our troops there and they're out of sight, what has that accomplished?"
Marines in Al Anbar province, the west-central region that is home to some of the most war-torn cities in the Sunni Arab heartland, appear to have taken that question to heart. Here, as elsewhere, field commanders are given wide latitude to make decisions on the ground, although commanders in the region and in Washington set overall policy, in keeping with U.S. and NATO military tradition.
Marine field commanders said the Qaim model would soon be repeated at bases across Al Anbar, with more Marines scheduled to leave heavily garrisoned encampments in Al Asad, Haditha and Hit to spread forces more evenly throughout the province's towns and villages.
"We'll have a continuing presence in these areas," said Col. W. Blake Crowe, commander of Marine forces in the western part of Al Anbar. "We won't populate every village -- we don't have enough force for that. But we'll continue to contest every town and village. We just need to contest them."
The idea behind the new campaign is to repeat the military's success last year in Tall Afar, where Army units cleared out insurgents and flooded the town with patrols and small-unit interactions with residents. Bush and others have touted the approach.