The secret dialogue has gone on since at least early 2006, but appeared to yield a tangible result only in the past week -- a relative calm in an area of western Baghdad that has been among the capital's most dangerous regions.
Talks have been complicated by the movement's internal divisions as well as the fiery cleric's public vow never to meet with Iraq's occupiers. Underlying the issue's sensitivity, Sadrists publicly deny any contact with the Americans or British -- fully aware the price of acknowledging such meetings would be banishment from the movement or worse.
The dialogue represents a drastic turnaround in the U.S. approach to al- Sadr and the militia loyal to him, the Mahdi Army. The talks seek to produce the same kind of marriage of convenience the military has reached across central Iraq with insurgent groups and Sunni tribes, many of whom once were prime supporters of Saddam Hussein. Both efforts are examples of how U.S. officials have sought to calm parts of Iraq by cooperating with groups they once considered untouchable.
Sunni militants cooperated in large part because they needed American help to battle militants aligned with al-Qaida in Iraq. By contrast, the Sadrists have yet to decide they want a clear break from their more radical and lawless elements.
In 2004, U.S. officials branded al- Sadr an outlaw and demanded his arrest, sparking two major Shiite revolts in Baghdad and southern Iraq that left hundreds dead in the shrine city of Najaf. Last year, as the Bush administration developed its "surge" strategy, military planners said the offensive would target Mahdi Army fighters involved in sectarian killings. American commanders later accused Iranian-backed elements of the Mahdi Army of being responsible for deadly bomb attacks against U.S. forces and of spearheading sectarian violence.
U.S. officials say they now feel they have no choice but to talk with the militia. Despite many internal rifts, al- Sadr's movement widely is seen as the most powerful force in Baghdad. The Mahdi Army's grip is absolute in most of the capital's Shiite neighborhoods, where it sells fuel and electricity and rents out houses, and it has reached deep inside the army and police. U.S. soldiers have marveled at the movement's ability to generate new leaders to replace almost every fighter they lock up.
American officials fear that failure to come to a political compromise with the Sadrists could resign the country to an even darker fate once U.S. forces begin to pull back.