WASHINGTON: President Barack Obama has given his national security team a new mission to end the war in Iraq, nearly six years after U.S.-led forces invaded, but he held off ordering a troop withdrawal right away to hear concerns and options from his military commanders.

Afghan President Hamid Karzai meets with U.S. Central Command chief General David Petraeus in Kabul, January 20, 2009.(Presidential Palace/Handout/Reuters) On his first full day in office, Obama summoned senior civilian and uniformed officials to the White House on Wednesday to begin fulfilling his campaign promise to pull combat forces out of Iraq in 16 months. Among those meeting with Obama was General David Petraeus, who had not seen him since the Nov. 4 election.

"I asked the military leadership to engage in additional planning necessary to execute a responsible military drawdown from Iraq," Obama said in a written statement after the meeting. He added that he planned to "undertake a full review of the situation in Afghanistan in order to develop a comprehensive policy for the entire region."

While the economy has overtaken Iraq on Obama's agenda, his opposition to the war was the original foundation of his presidential race, and ending it stands as perhaps the most salient test of his commitment to his campaign promises. Yet fulfilling his pledge also could put him at odds from the start with generals who worry that acting too quickly may jeopardize the progress achieved since President George W. Bush sent in more forces and Petraeus revamped the strategy two years ago.

The meeting on Wednesday served mainly to brief Obama on the state of affairs in Iraq. He heard from General Ray Odierno, the commander of forces in Iraq, who participated by secure videoconference from Baghdad, and the departing U.S. ambassador, Ryan Crocker. The session did not focus on specific withdrawal proposals but instead featured a broad discussion of the political climate and security situation, according to senior officials.

Among the topics were the challenges as Iraq moves through a series of critical elections this year and the required changes to the location, size and mission of the American military force under a new agreement between Washington and Baghdad, the officials said. Petraeus also weighed in on the regional implications of Iraq.

Military planners have prepared a series of possible withdrawal plans that, in the words of one official, "range from conservative to aggressive." One of them matches the president's 16-month timetable, although Obama always envisioned a substantial "residual force" remaining beyond that to train Iraqi forces and hunt terrorist cells.

Senior officials said another proposal for a more gradual withdrawal was drawn up to meet the terms of the agreement recently sealed by Bush and Iraqi officials, which requires the United States to pull combat forces out of Iraqi cities by June and to withdraw all troops by the end of 2011.

Odierno initially favored withdrawing just two of the remaining 14 combat brigades by summer or fall, and military planners drew up a faster option only in recent weeks, on the assumption that Obama would ask for it. But a number of senior officers have warned about the risks of a rapid withdrawal, military officials said.

Since the election, Obama has reaffirmed his intention to end the war, while leaving room to rethink the details by saying he would listen to his commanders before issuing any orders. In his inaugural address on Tuesday, Obama said, "We will begin to responsibly leave Iraq to its people."

Aides said he was taking a cautious approach to make sure that his promise would be executed effectively and safely for the troops.

Some opponents of the war said they planned to hold Obama to his campaign promise. "I take him at his word," said Tom Andrews, national director of Win Without War, a group opposing the Iraq conflict. "He could not have been clearer as a candidate."

At the same time, some veterans of the Bush White House warned against making precipitous moves, or even changing the mission. Peter Feaver, a former national security aide to Bush, said a key to the turnaround in Iraq in the past two years was the decision to redefine the mission, focusing it on protecting the civilian population.

"It may sound like an easy thing to do, and it is certainly the president's call," said Feaver, now a professor at Duke University. "But there are risks associated with changing the mission, so it shouldn't be done lightly."

Nonetheless, Obama and his advisers said it was important to signal a commitment from his presidency's inception. While campaigning last summer, Obama said: "My first day in office, I will bring the Joint Chiefs of Staff in, and I will give them a new mission." Although he did not call in the Joint Chiefs, their chairman, Admiral Mike Mullen, was at the Wednesday meeting, and Obama is expected to meet in the coming days with the rest of the Joint Chiefs.