WASHINGTON (AP) -- President Barack Obama, in a meeting with his top national security advisers Wednesday, asked the Pentagon to do whatever additional planning is necessary to "execute a responsible military drawdown from Iraq."

Obama's statement, issued by the White House after the gathering, opened his much-anticipated effort to withdraw troops more swiftly than the previous administration had proposed. It made no reference to any timeline or his campaign vow to get combat troops out of Iraq in 16 months.

"The meeting was productive and I very much appreciated receiving assessments from these experienced and dedicated individuals," Obama said. "During the discussion, I asked the military leadership to engage in additional planning necessary to execute a responsible military drawdown from Iraq."

He added that he would soon travel to the Pentagon and meet with the Joint Chiefs of Staff.

A senior military official, speaking on condition of anonymity because the schedule is not confirmed, said that meeting with the Joint Chiefs - the president's senior uniformed military advisers - would come within a week.

"We will undertake a full review of the situation in Afghanistan in order to develop a comprehensive policy for the entire region," Obama said.

Wednesday's strategy session included Obama and Vice President Joe Biden, both critics of the management of the war. Officials familiar with the meeting declined to disclose details of what was discussed.

"This is a logical first step for a new president that wants to learn about or to speak to the people that are most directly involved," Pentagon spokesman Bryan Whitman said.

The White House meeting was part of a symbolic framing of a new president's agenda on his first full day in office, but it did not completely fulfill Obama's oft-repeated pledge to bring in the Joint Chiefs of Staff on his first day in office and order a close to a war he opposed.

Shutting down the war will be more complicated than that, and the Joint Chiefs are not the only players.

The agenda as announced by the White House included the U.S. ambassador in Iraq, Ryan Crocker; another State Department representative and Gen. David Petraeus, who is responsible for managing both the Iraq and Afghanistan wars.

The chairman of the Joint Chiefs, Adm. Mike Mullen, attended along with Defense Secretary Robert Gates. Both are holdovers from the Bush administration, now getting new instructions.

The top general in Iraq, Gen. Raymond Odierno, was participating by video hookup. He has already drawn up one set of withdrawal plans but would have to get things moving faster if he is to meet Obama's timetable.

The agenda for Obama's White House meeting changed several times. At one point it was to include a broader look at the war in Afghanistan, which Obama has said was hobbled by a misguided focus on Iraq.

The Pentagon first said that the top commander in Afghanistan would participate, and then said he would not.

Ali al-Dabbagh, a spokesman for the Iraqi prime minister, told Associated Press Television News on Tuesday that Iraq is willing to have the U.S. withdraw its troops and assume security for the country "before the end of 2011," the departure date agreed to by former President George W. Bush in November.

Senior military leaders had been wary of any timeline, saying that withdrawal plans should be keyed to continued security improvements, but have said that they could meet either the deadline set with Iraq or the shorter one Obama wants.

There are currently about 143,000 U.S. forces in Iraq, as many as 8,000 more than were there before the troop buildup, which began in early 2007 and contributed in part to the decline in violence. There are about 34,000 U.S. troops in Afghanistan, including 17,000 in the NATO-led coalition and another 17,000 fighting insurgents and training Afghan forces.

---

Associated Press writers Pauline Jelinek and Matthew Lee contributed to this report.