Obama's plan would pull out all combat troops 19 months after his inauguration, although he had promised repeatedly during the 2008 campaign that he would withdraw them 16 months after taking office. That schedule, based on removing roughly one brigade a month, was predicated on commanders determining that it would not endanger U.S. troops left behind or Iraq's fragile security.
Pledging to end the war in 16 months helped to build enormous grass-roots support for Obama's White House bid.
The withdrawal plan - an announcement could come as early as this week - calls for leaving a large contingent of troops behind, between 30,000 and 50,000 troops, to advise and train Iraqi security forces and to protect U.S. interests.
They would still be capable of conducting combat operations and would be able to call in strikes from carrier- or land-based aircraft, reports CBS News national security correspondent David Martin.
Also staying beyond the 19 months would be intelligence and surveillance specialists and their equipment, including unmanned aircraft, according to two administration officials who spoke on condition of anonymity because the plan has not been made public.
The complete withdrawal of American forces will take place by December 2011, the period by which the U.S. agreed with Iraq to remove all troops.
A senior White House official said Tuesday that Obama is at least a day away from making a final decision. He further said an announcement on Wednesday was unlikely, but he said that Obama could discuss Iraq during a trip to North Carolina later this week.
A Pentagon official confirmed to CBS News that Mr. Obama is going to Camp Lejuene, N.C. on Friday where he is expected to announce his Iraq plan. Many of the Marines at Lejuene were scheduled to go to Iraq, but are now bound for Afghanistan as part of the 17,000 troop buildup, Martin reports.
About 142,000 U.S. troops are in Iraq, roughly 14 brigades, about 11,000 more than the total in Iraq when President George W. Bush announced in January 2007 that he would "surge" the force to put down the insurgency. He sent an additional 21,000 combat troops to Baghdad and Anbar province.
Although the number of combat brigades has dropped from 20 to 14, the U.S. has increased the number of logistical and other support troops. A brigade is usually about 3,000 to 5,000 troops.
Obama's campaign promise to withdraw troops in 16 months was based on a military estimate on what would be an orderly pace of removing troops, given the logistical difficulties of removing so many people and tons of equipment, a U.S. military official said.
The 19-month strategy is a compromise between commanders and advisers who are worried that security gains could backslide in Iraq and those who think the bulk of U.S. combat work is long since done.
- one that followed Obama's 16-month timeline and one that stretched withdrawal over 23 months, The Associated Press reported earlier this month.
By choosing 19 months, the president is not locked into a hard and fast timetable - he can always slow it down if conditions on the ground get worse, reports Martin.
Some U.S. commanders have spoken more optimistically in recent months about prospects for reducing the force.
Marine Maj. Gen. John Kelly, who just left his job overseeing U.S. operations in Anbar Province, said Tuesday that he saw violence drop to an almost "meaningless" level over the past year.
Kelly told reporters Tuesday that in the area that was the home ground of the Sunni insurgency, American combat forces don't have enough to do and most could have pulled out months ago.
"There is still a security issue there, but in the province I just left the (Iraqi) army and the police are more than handling the remnants of what used to be al Qaeda," Kelly said. "There's other parts of Iraq that aren't going quite as well but all of Iraq is doing pretty well."
According to officials, Obama had requested a range of options from his top military advisers, including one that would have withdrawn troops in 16 months. Defense Secretary Robert Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, had recently forwarded withdrawal alternatives to the White House for Obama's consideration.
In addition to the U.S. troops to be withdrawn, there is a sizable cadre of contractors who provide services to them who would pack their bags as well. There were 148,050 defense contractor personnel working in Iraq as of December, 39,262 of them U.S. citizens.
There are more than 200 U.S. military installations in Iraq. According to Army officials interviewed by the Government Accountability Office, it can take up to two months to shut down small outposts that hold up to 300 troops. Larger entrenched facilities, like Balad Air Base, could take up to 18 months to close, according to the GAO.
As of Monday, at least 4,250 members of the U.S. military had died in the Iraq war since it began in March 2003, according to an Associated Press count. More than 31,000 have been injured. An additional 35,841 have received medical air transport due to non-hostile incidents.
Congress has approved more than $657 billion so far for the Iraq war, according to a report last year from the Congressional Research Service.