WASHINGTON — President Barack Obama is expected to order all U.S. combat troops to leave Iraq by August of next year, administration officials said, closing the door on a war that has led to the deaths of at least 4,250 American soldiers.

The pullout recommended by Obama's security advisers would free up troops and resources for the war in Afghanistan, where Obama has said the threat to national security is acute. The Iraq withdrawal would be completed 18 months from now.

"We are now carefully reviewing our policies in both wars, and I will soon announce a way forward in Iraq that leaves Iraq to its people and responsibly ends this war," Obama said in his address to Congress on Tuesday.

An announcement could come as early as this week, a senior White House official said Tuesday, adding that Obama has not yet approved the final details. The official, who spoke on condition of anonymity because an announcement was not yet planned, said Obama could discuss Iraq during a trip to North Carolina on Friday.

Obama built enormous grass-roots support for his White House bid by promising a quick end to the unpopular Iraq war. His 16-month withdrawal plan, based on removing roughly one brigade a month, had been predicated on commanders determining that it would not endanger U.S. troops left behind or Iraq's fragile security.

Officials said that upon entering the White House, Obama requested a range of options from his top military advisers, asking for plans ranging between 16 to 23 months.

Defense Secretary Robert Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, had recently forwarded three withdrawal alternatives for Obama's consideration — 16, 19 and 23 months, the longest an alternative preferred by Iraqi officials and some of Obama's Iraq-based generals. The 19-month plan, which was selected, was pegged to his January inauguration.