Administration officials said Mr. Obama would most likely pull out the entire 30,000 troops by the end of 2012. What is still not known is how soon and how fast, though as the administration’s deliberations wind down, the outlines of the main proposals are becoming clearer.

Some senior White House officials advocate a plan under which 15,000 troops would return by the end of this year and the other 15,000 by the end of 2012, said an official who was briefed on the deliberations. Backers of this timetable include retired Lt. Gen. Douglas E. Lute, the president’s senior adviser on Afghanistan.

Vice President Joseph R. Biden Jr., who has long pushed for the United States to curtail its military engagement in Afghanistan, favors a plan under which all 30,000 troops would be pulled out within 12 months, said this official, who spoke on the condition of anonymity to discuss internal conversations.

Defense Secretary Robert M. Gates has said that the initial withdrawal should be modest, and that substantial combat forces should remain into next year’s fighting season so as not to risk successes earned through the surge.