WASHINGTON -- President Barack Obama announced Friday that U.S. troops in Afghanistan will assume a "support role" starting this spring, focusing on an advisory and training mission before a withdrawal of most American forces by the end of 2014.

Obama said the U.S. military will still engage in battlefield fighting when necessary, but Afghan forces will take the lead in security in an accelerated fashion. However, the president stopped short of committing to a faster timetable for the American troop withdrawal.

"It will be a historic moment and another step toward full Afghan sovereignty," Obama said during a news conference with Afghan president Hamid Karzai at the White House.

"Our presence, the nature of our work, will be different," he said. "We will be in a training, assisting, advising role."

Obama made his remarks after meeting with Karzai for several hours to begin establishing guidelines for the handover. The president said he will consult with U.S. generals over the specifics of the withdrawal and about how many troops, if any, to leave in Afghanistan in 2015 and beyond.

Within the White House, some officials are pushing to keep a force as small as 2,500 past 2014 to help train and support the Afghans, far lower than the 10,000 to 30,000 that some U.S. officials and NATO allies were discussing a year ago. Senior aides this week did not rule out withdrawing all troops in 2015.

Obama declared twice during the news conference that the end of 2014 would mark the "responsible" end of a war that began in response to the Sept. 11, 2001, attacks on the United States by Osama bin Laden's al-Qaida terrorist network.

Asked if the cost of the war, in money and lives lost, was worth it, Obama reminded the audience of reporters and staff in the East Room, along with a television audience, of the 3,000 Americans who were "viciously murdered" by al-Qaida, as well as the Afghans who were "brutalized" by the Taliban.

"We achieved our central goal, or have come very close to achieving our central goal, which is to decapacitate al-Qaida, to dismantle them, to make sure that they can't attack us again," Obama said.

But, he added, "Have we achieved everything some might have imagined us achieving in the best of scenarios? Probably not. This is a human enterprise, and you fall short of the ideal."

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