Yet many Iraqis have told reporters they still do not feel secure, despite General Petraeus’s charts showing drops in violence. Internal displacement has doubled since the “surge” began, reaching 1.1 million people nationwide, according to the International Office of Migration and the Iraqi Red Crescent Society.

Shiite militias have continued their steady march to force Sunni Arabs from an ever-expanding area of Baghdad and surrounding villages. That has been compounded by mass roundups of Sunni Arabs suspected of being insurgents, who are held for months in dangerously crowded detention centers without trial or charges. Shiite judges concede that 40 percent to 50 percent of those detainees are innocent.

Meanwhile, fighting within sects is on the rise.

Shiites have sunk into a violent struggle between factions loyal to rival clerics, Abdel Aziz Hakim and Moktada al-Sadr. Two provincial governors in the Shiite south were assassinated in August, in Muthanna and Diwaniya Provinces. Both were members of the Supreme Islamic Iraqi Council, led by Mr. Hakim.

Assassinations and other attacks have persisted for months in the south, including the outbreak of fighting in Karbala barely two weeks ago between factions loyal to the clerics. Mr. Crocker interpreted the fighting, which left at least 52 people dead, as a catalyst to a cease-fire by Mr. Sadr’s forces.

However, Mr. Sadr’s word has rarely proved effective or lasting. He issued a similar command in February at the start of the American troop increase in Baghdad, and after a hiatus of a few weeks, the killings of Sunni Arabs resumed, although at a lower level, and so did the sectarian purging of neighborhoods.

Among Sunni Arabs, the divide splits those in Parliament who were early participants in the political process and the tribal sheiks in Sunni-majority areas, notably Anbar Province, who have recently become American allies and rivals for power.

This struggle adds yet more uncertainty to the fraught political situation. Power has essentially shifted in a number of directions, geographically and socially. Some provinces have become dominions unto themselves; other provinces are impoverished, unable to get Baghdad to deliver resources that the provinces can not procure themselves.