(Adds quotes, background)
By Andrew Gray
WASHINGTON Jan 22 The new U.S. administration has not yet decided whether to withdraw combat troops from Iraq in 16 months, as proposed by President Barack Obama during his election campaign, senior officials said on Thursday.
Defense Secretary Robert Gates said he and other advisers were studying a range of options on how quickly to pull out of Iraq, including the 16-month timetable.
But both Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, declined to say whether they supported the timeline suggested by Obama when he was running for president.
"We have begun a process in which a variety of options are being examined," Gates told reporters at the Pentagon.
Obama met with Gates, senior military officers and the U.S. ambassador to Iraq on Wednesday, his first full day in office, to discuss the war, which the president opposed and which made his predecessor George W. Bush deeply unpopular.
Both Gates, who oversaw a dramatic improvement in U.S. fortunes in Iraq in the last years of the Bush administration, and senior military officers have urged a cautious approach to troop cuts, fearing security gains could be lost.
Gates said there was "a good give-and-take" at the White House meeting.
"Our obligation is to give the president a range of options and the risks associated with each of those options," Gates said.
"He will make the decision and we will execute it."
Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, told the same Pentagon news briefing that he envisioned a rapid process to present Obama with options and allow him to make decisions on troop levels in both Iraq and Afghanistan.
The United States has some 143,000 troops in Iraq, nearly six years after U.S.-led forces invaded the country deposed Saddam Hussein. More than 4,220 U.S. troops and tens of thousands of Iraqis have died in the conflict.
In his campaign for the Democratic presidential nomination and for the presidency, Obama stressed his opposition to the war and promised a timetable for withdrawing U.S. combat troops, which he suggested could be done in 16 months.
He has, however, also left room for maneuver by stressing that he wants a responsible withdrawal, that he will listen to commanders' advice and that he will leave a "residual force" in Iraq even after those labeled combat troops have gone.
Under a security pact between the United States and Iraq which came into force at the start of this year, all U.S. forces must be out of the country by the end of 2011.
Obama has pledged to focus more on Afghanistan, where insurgent violence has risen dramatically over the past two years. The United States has some 34,000 troops in Afghanistan, about half them operating as part of a NATO-led force.
(Editing by Cynthia Osterman)