WASHINGTON – The United States plans to withdraw most of its troops from Iraq by August 2010, according to Obama administration officials.

The withdrawal plan would fulfill one of President Obama’s central campaign pledges, albeit a little more slowly than he promised. He said he would withdraw troops within 16 months, roughly one brigade a month from the time of his inauguration. August 2010 would be 19 months.

The officials said they expect Obama to make the announcement this week.

The US military will leave behind a residual force, between 30,000 and 50,000 troops, to continue advising and training Iraqi security forces, the two officials said. Also staying beyond the 19 months will be intelligence and surveillance specialists and their equipment, including unmanned aircraft, they said.

A further withdrawal will take place before December 2011, the period by which the United States agreed with Iraq to remove all American troops.

A senior White House official said yesterday that Obama is at least a day away from making a final decision. He further said an announcement today was unlikely, but he said that Obama could discuss Iraq during a trip to North Carolina on Friday.

About 142,000 US troops are in Iraq, roughly 14 brigades, about 11,000 above the total in Iraq when then-President George W. Bush announced in January 2007 that he would start a “surge” in forces 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 United States has increased the number of logistical and other support 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 US military official said.

The 19-month strategy is a compromise between commanders and advisers worried that security gains could backslide in Iraq, and those who think the bulk of US combat work is long done.