President Bush has long resisted a timetable for pulling out, even under heavy pressure from a nation distressed by American deaths and discouraged by the length of the war that began in 2003. But that has softened in recent weeks.
The timing has major political importance in both Iraq and the United States.
The two contenders to replace Bush as commander in chief, Republican John McCain and Democrat Barack Obama, spar almost daily over the future course of the war.
Obama wants all U.S. combat forces out of Iraq within 16 months of his taking office, saying they are needed more urgently in Afghanistan. McCain says recent security improvements in Iraq show that decisions on the timing of further pullouts should be determined by circumstances on the ground rather than by prearranged timetables - a position the White House has vigorously held until recently.
The administration has inched toward the Iraqi view that setting at least a target date for withdrawal would make it politically palatable for Iraq's government to accept a substantial U.S. troop presence beyond this year.
The rationale for the pullout is that Iraqi security forces will be ready to stand on their own, although it remains possible that some U.S. military training role would continue. In Iraq, provincial elections are supposed to be held later this year, followed by national balloting in 2009.