WASHINGTON — A new military plan for troop withdrawals from Iraq that was described in broad terms this week to President-elect Barack Obama falls short of the 16-month timetable Mr. Obama outlined during his election campaign, United States military officials said Wednesday.

The plan was proposed by the top American commanders responsible for Iraq, Gen. David H. Petraeus and Gen. Ray Odierno, and it represents their first recommendation on troop withdrawals under an Obama presidency. While Mr. Obama has said he will seek advice from his commanders, their resistance to a faster drawdown could present the new president with a tough political choice between overruling his generals or backing away from his goal.

The plan, completed last week, envisions withdrawing two more brigades, or some 7,000 to 8,000 troops, from Iraq in the first six months of 2009, the military officials said. But that would leave 12 combat brigades in Iraq by June 2009, and while declining to be more specific, the officials made clear that the withdrawal of all combat forces under the generals’ recommendations would not come until some time after May 2010, Mr. Obama’s target.

Transition officials said the plan was described in only general terms to Mr. Obama by Robert M. Gates, who is staying on as defense secretary, and Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, when Mr. Obama met for five and a half hours with his national security team on Monday in Chicago. They said all participants had sidestepped the details of how to reconcile Mr. Obama’s timetable for withdrawing combat forces with the more extended one recommended by the generals. A transition official said that in future meetings, “the military will get a chance to articulate their preferences.”

In the campaign, Mr. Obama said he would not hesitate to overrule his commanders. By early December, however, he signaled some flexibility when he said that he still wanted combat troops out of Iraq in 16 months but that he would also listen to the recommendations of his generals. Mr. Gates has expressed confidence that he and Mr. Obama might reach common ground. But in discussing the new plan, senior military officials nonetheless made clear that they were not comfortable with the time frame Mr. Obama articulated in the campaign. “Sixteen months is going to be tough,” said one senior military officer who was briefed on the plan. “We are not quite there yet.”

Those at the Chicago meeting included Hillary Rodham Clinton, Mr. Obama’s choice for secretary of state; Vice President-elect Joseph R. Biden Jr.; Gen. James L. Jones, who is to be Mr. Obama’s national security adviser; Susan E. Rice, who is to be ambassador to the United Nations; Rahm Emanuel, who will be White House chief of staff; Gregory B. Craig, who will be White House counsel; James B. Steinberg, who is expected to be deputy secretary of state; Thomas E. Donilon, who is expected to be General Jones’s deputy; and Anthony Blinken, a senior foreign policy adviser to Mr. Biden.

Mr. Obama apparently did not ask Mr. Gates or Admiral Mullen for specifics on withdrawals, according to people briefed on the discussions. “There was not challenging or questioning of any particular timetable,” a transition official said. “There wasn’t a point on which there was any pushback from either side.”

For his part, Geoff Morrell, the Pentagon press secretary, said that Mr. Gates had left the Chicago meeting feeling that “they had an excellent discussion, and excellent chemistry as well.”

The plan drafted by General Odierno and General Petraeus was drawn up to meet the so-called status of forces agreement between the United States and Iraqi governments that calls for all American forces to be out of Iraq by the end of 2011 and all combat troops out of Iraqi cities by June 2009. The agreement sets forth both a shorter and longer timetable than Mr. Obama’s campaign pledge, with some combat forces out sooner but all forces out later.

One way commanders say they will try to meet that first deadline is by effectively reassigning combat troops to training and support of the Iraqis, even though the difference would be in some cases semantic because armed American troops would still go on combat patrols with their Iraqi counterparts.

The participants at the Chicago meeting did discuss the deadline for all American combat troops to be withdrawn from Iraqi cities by June, as outlined in the agreement with the Iraqi government. A person familiar with the talks said those at the meeting discussed whether the Iraqis would allow “remissioned” combat forces to remain in Iraqi cities after June. Mr. Gates and Admiral Mullen did not rule out the idea that Iraqis might permit such troops, the person said.

In a briefing to reporters last week in Balad, Iraq, General Odierno said that some American forces would remain in a support role in Iraqi cities beyond the June deadline. He said that the troops would be deployed at numerous security outposts in urban areas to help support and train Iraqi forces. “We’ll maintain our very close partnership with the Iraqi security forces throughout Iraq even after the summer,” he said.

General Odierno said that it was particularly important for American troops to support Iraqis in 2009, when three elections, at the provincial, district and national levels, are scheduled. “It’s important that we maintain enough presence here that we can help them through this year of transition,” he said.

General Odierno also said that he was planning for all American forces to be out of Iraq by 2011, as called for in the agreement with the Iraqi government, but he said the agreement could be renegotiated. “Three years is a long time,” General Odierno said.

The new military plan allows for the fact that negotiations could eventually call for American troops in Iraq after 2011, but it does not put a number on that force, a person familiar with its details said.

Other topics discussed at the meeting in Chicago included Afghanistan, Pakistan, the Middle East, the detainees at Guantánamo Bay and how the national security policy-making process in the Obama administration will work.

Helene Cooper contributed reporting.