WASHINGTON - THE biggest constraint Mr Obama faces on Iraq is an agreement between Baghdad and Washington signed before he took office, which requires that all US forces depart the country by the end of 2011.
Any change to that deal would require negotiations with the Baghdad government in that country's fraught political climate.
During the campaign, Mr Obama said he would maintain a residual force on the ground to train Iraq forces, fight extremists and protect US assets.
Mr Obama has made clear he inherited the war in Iraq from his predecessor George W. Bush, but he is keen to ensure that a withdrawal does not undermine hard-won gains in the strategic, oil-rich country that neighbors Iran.
Although the 19-month option would be a little slower than his campaign pledge, Mr Obama would still put an end to a war nearing its sixth anniversary that has profoundly divided the American public.
The war has cost hundreds of billions of dollars and over 4,200 American lives.
With Iraq fading as a concern as the country faces its worst recession in decades, 61 per cent of Americans last month said they thought the war was not worth its cost, an ABC News-Washington Post poll found.
Polls also show that most Americans back Mr Obama's argument that US troops can best be used to fight the war in Afghanistan, which Mr Obama has called 'the central front' in the war on terror.
The Iraq drawdown is expected to allow more US troops to be deployed to Afghanistan, where Mr Obama has recently authorised an increase of 17,000 troops to add to the 36,000-strong US force there.
Administration officials have also indicated that a withdrawal from Iraq would help toward halving the trillion-dollar-plus US budget deficit by the end of Mr Obama's first term in 2013.
In an address to Congress late Tuesday, Mr Obama said he was 'now carefully reviewing our policies in both wars.
'I will soon announce a way forward in Iraq that leaves Iraq to its people and responsibly ends this war,' he said.