Abu Ali walked into the Americans’ battle-scarred combat outpost with an unusual proposal: the community leader was worried about the insurgents, and wanted the soldiers’ help in taking them on.

The April 7 meeting was the beginning of a new alliance and, American commanders hope, a portent of what is to come in the bitterly contested Diyala Province.

Using his Iraqi partners to pick out the insurgents and uncover the bombs they had seeded along the cratered roads, Captain Richards’s soldiers soon apprehended more than 100 militants, including several low-level emirs. The Iraqis called themselves the Local Committee; Captain Richards dubbed them the Kit Carson scouts.

“It is the only way that we can keep Al Qaeda out,” said Captain Richards, who operates from a former Iraqi police station in the Buhritz sector of the city that still bears the sooty streaks from the day militants set it aflame last year.

The American military has struggled for more than four years to train and equip the Iraqi Army. But here the local Sunni residents, including a number of former insurgents from the 1920s Revolution Brigades, have emerged as a linchpin of the American strategy.

The new coalition reflects some hard-headed calculations on both sides. Eager for intelligence on their elusive foes, American officers have been willing to overlook the past of some of their newfound allies.

Many Sunnis, for their part, are less inclined to see the soldiers as occupiers now that it is clear that American troop reductions are all but inevitable, and they are more concerned with strengthening their ability to fend off threats from Sunni jihadists and Shiite militias. In a surprising twist, the jihadists — the Americans’ most ardent foes — made the new strategy possible. Al Qaeda in Mesopotamia, a predominantly Iraqi organization with a small but significant foreign component, severely overplayed its hand, spawning resentment by many residents and other insurgent groups.

Imposing a severe version of Islamic law, the group installed its own clerics, established an Islamic court and banned the sale of cigarettes, which even this week were nowhere to be found in the humble shops in western Baquba to the consternation of patrolling Iraqi troops.

The fighters raised funds by kidnapping local Iraqis, found accommodations by evicting some residents from their homes and killed with abandon when anyone got in their way, residents say. A small group of bearded black-clad militants took down the Iraqi flag and raised the banner of their self-proclaimed Islamic State of Iraq.

“They used religion as a ploy to get in and exploit people’s passions,” said one member of the Kit Carson scouts, who gave his name as Haidar. “They were Iraqis and other Arabs from Syria, Afghanistan, Jordan, Saudi Arabia and Egypt. They started kicking people out of their houses and getting ransom from rich people. They would shoot people in front of their houses to scare the others.”

Collaborations like the one with the scouts in Baquba are slowly beginning to emerge in other parts of Iraq. In Baquba they face some notable obstacles, primarily from the Shiite-dominated provincial and Baghdad ministries that are worried about American efforts to rally the Sunnis and institutionalize them as a security force.

But with Prime Minister Nuri Kamal al-Maliki’s government showing scant progress toward political reconciliation and the American military eager to achieve a measure of stability before its elevated troop levels begin to shrink, American commanders appear determined to proceed with this more decentralized strategy — one that relies less on initiatives taken by Iraqi leaders in Baghdad and more on newly forged coalitions with local Iraqis.

A West Point graduate, Idaho native and former Mormon missionary who worked for two years with Chinese immigrants in Canada, Captain Richards commands Bronco Troop, First Squadron, 14th Cavalry Regiment. When the 31-year-old officer was first sent to Buhritz in mid-March as part of a battalion-size task force, he encountered a deeply entrenched foe who numbered in the thousands.