RAMADI, Iraq — Meeting neighbors and supplicants on a recent night, America’s staunchest ally in Iraq, Sheik Ahmed Abu Risha, sat in a tent sipping tea. He greeted each visitor with a hearty outburst of “dear one” and a kiss on the cheek.

At one point a young man with an M-16 riflekissed the sheik on the cheek, too, in a clear sign of loyalty from a member of a tribal militia.

Abu Risha is often credited with helping turn the tide of the Iraq war in 2006 by rallying local tribal leaders to fight al-Qaida in Mesopotamia, the homegrown affiliate in Iraq. He says he still commands about 80,000 militia members.

Two weeks before the U.S. military completes its withdrawal from Iraq, these units, known broadly as the Sunni Awakening, still remain outside the new Iraqi police force and army. Ragtag groups of men wearing jeans and carrying rifles at dusty checkpoints across western Iraq, they are a loose end left by the United States.

Some Awakening members, by their own admission, are former insurgents and members of Saddam Hussein’s Baath Party who fought in a nationalist wing of the Sunni uprising early in the war, a matter of grave concern to the Shiite-dominated government of Prime Minister Nouri Kamal al-Maliki. Without the buffer provided by the Americans, relations between the Awakening and the central government, always touchy, are growing increasingly strained, and the government now wants the Awakening to disband by Dec. 31, the deadline for the exit of the U.S. military.

Abu Risha, in an interview in his compound beside a lazy bend in the Euphrates River, said members of the tribal militias in western Iraq were not likely to disarm quickly — and certainly not by the end of the month.

“I don’t think the Awakening members will give up their weapons,” he said, contending that the problem was a lack of government-provided protection against al-Qaida. “They want to defend themselves. The weapons they carry are their personal weapons.”

In the tradition of the endless negotiations, feints and shifting alliances of desert tribes, the Sunni chieftains in Anbar province unexpectedly switched sides in 2006 and 2007, in perhaps the most important single step for establishing stability here after the war and the insurgency. Once brought over to the American side, they were an enormous help in hunting down their former insurgent allies, members of the Islamic militias, including al-Qaida.

A new Sunni-Shiite rift

But the pendulum is now swinging back toward repression of Baathists, something being discussed over tea in places like Abu Risha’s tent, pitched in the courtyard of his fortresslike compound.

The Shiite-dominated central government has arrested prominent Sunnis on accusations that they are secret members of the long-disbanded Baath Party, which has alienated Sunni elites. Meanwhile, a Sunni revolt a few hundred miles to the north of here against the Shiite-aligned government in neighboring Syria is gathering force.

Last month, government police officers wounded two guards and detained two others in a raid on the home of a Sunni, Sheik Albo Baz, in Salahuddin province, prompting a protest by several thousand Sunnis in Samarra, a city that is tense and divided by sect.

This followed the roundup by police officers of 600 suspected Baath Party sympathizers in October; they were accused of planning a coup.

Distressingly for Sunnis, the government paraded some of those arrested on state television in a bizarre spectacle: Relatives of their supposed victims were invited into the room and screamed at the suspects, and demanded their execution. Such a program was a tradition on Hussein’s state television, though the suspects then were more likely to be Shiites.

A plot unveiled?

Mohammad Rida, a member of the Sadrist party in Iraq’s parliament, said in an interview that the government had documents indicating that Baath Party sleeper cells intended to stage a coup after the American withdrawal. The police obtained the names of hundreds of conspirators in a confession by a former Baathist detained in July, he said.

In addition, Rida said, documents found in the ruins of the Libyan intelligence office after the fall of Tripoli, and handed over to the Iraqis, corroborated the plot. “Iraq did what any other country would do,” he said. “We responded.”

Abu Risha’s compound is less than a mile from what used to be Camp Blue Diamond, home of the young U.S. Army officers who first struck up a friendship with him, and who brought him to the American side. (A grandfather of Abu Risha’s had chosen a different path, choosing to fight the British occupation in the 1920s.)

About 30,000 former Awakening militia members have received jobs in the Anbar police, and thousands more have entered the army.

Abu Risha said about 80,000 remained in irregular tribal-based units. The central government has put the figure at 50,000 remaining Awakening fighters.