White House officials expressed confidence that the transfer to civilians  about 2,400 people who would work at the Baghdad embassy and other diplomatic sites  would be carried out on schedule, and that they could fulfill their mission of helping bring stability to Iraq.

“The really big picture that we have seen in Iraq over the last year and a half to two years is this: the number of violent incidents is significantly down, the competence of Iraqi security forces is significantly up, and politics has emerged as the basic way of doing business in Iraq,” said Antony J. Blinken, the national security adviser to Vice President Joseph R. Biden Jr. “If that trend continues, and I acknowledge it is an ‘if,’ that creates a much better context for dealing with the very significant and serious problems that remain in Iraq.”

But the tiny military presence under the Obama administration’s plan  limited to several dozen to several hundred officers in an embassy office who would help the Iraqis purchase and field new American military equipment  and the civilians’ growing portfolio have led some veteran Iraq hands to suggest that thousands of additional troops will be needed after 2011.

“We need strategic patience here,” Ryan C. Crocker, who served as ambassador in Iraq from 2007 until early 2009, said in an interview. “Our timetables are getting out ahead of Iraqi reality. We do have an Iraqi partner in this. We certainly are not the ones making unilateral decisions anymore. But if they come to us later on this year requesting that we jointly relook at the post-2011 period, it is going to be in our strategic interest to be responsive.”

The array of tasks for which American troops are likely to be needed, military experts and some Iraqi officials say, include training Iraqi forces to operate and logistically support new M-1 tanks, artillery and F-16s they intend to acquire from the Americans; protecting Iraq’s airspace until the country can rebuild its air force; and perhaps assisting Iraq’s special operations units in carrying out counterterrorism operations.