"I've been listening to the campaign, and I understand," Mullen said. "And he has certainly reinforced that since the election, so from a planning standpoint, we are looking at that as well."
Mullen, once a critic of Obama's plan to pull combat forces from Iraq in 16 months, said the Pentagon has already identified and practiced travel routes out of Iraq along exit routes through Turkey and Jordan.
The governments in those two bordering countries are U.S. allies, and Mullen said they support the withdrawal planning effort.
Mullen, who is halfway through a two-year term, said he expects to stay on next year as the new administration takes office, adding, "We all serve at the pleasure of the president. I'll serve as long as he wants me to."
Obama has said he wants to assemble a national security team quickly. He has not yet named a candidate for defense secretary — the top civilian leader at the Pentagon.
The current defense secretary, Robert Gates, is often mentioned as an option for Obama. If Gates stayed it would provide the continuity and stability Obama has said he wants in his national security operations, but neither man has discussed the possibility publicly.
Pentagon officials, including Mullen, have consistently rejected timelines for pulling troops out of Iraq, saying that any withdrawal must be based on security conditions in Iraq. At the same time, military leaders have said they need 15,000 to 20,000 more troops in Afghanistan — including four more combat brigades.
Obama, who has called Afghanistan an "urgent crisis," said in a speech Oct. 22 that "it's time to heed the call" from U.S. Gen. David McKiernan, the commander of NATO forces in Afghanistan, for more U.S. troops. Obama said he would send at least two or three additional combat brigades. One combat brigade typically has 3,500-4,000 soldiers.
Obama also has called for more training of Afghan security forces as well as more nonmilitary assistance.
Mullen said he is working to get as many troops into Afghanistan as quickly as possible and noted he's not surprised that Taliban leaders said this week that they would not entertain settlement talks with the Afghan government as long as foreign forces remained in the country.
"It's my belief that you negotiate from a position of strength and right now the Taliban is doing pretty well," said Mullen. "I think that's important as we discuss how we negotiate, and with whom we negotiate, that we do so from a position of strength."
Mullen would not disclose how many combat brigades and additional support forces he will be able to get to Afghanistan by next spring, when the military expects to face another offensive by militants.
While Mullen acknowledged that troops in the northern city of Mosul are still in a tough fight, he said commanders are confident that they will be able to turn the city over to the Iraqis by next June.
Under the security agreement now before the Iraqi Parliament, U.S. troops must be out of the cities by June 2009, and leave Iraq by the end of 2011.
Giving the Iraqis control of Baghdad will also be doable, but challenging, he said.
While violence has plunged in the capital city, there are still frequent, dramatic attacks, more often targeted at Iraqi citizens.
He also has to address logistical challenges in removing forces from Iraq. Noting the huge amount of equipment and infrastructure under the U.S. flag in Iraq, Mullen said planners are looking at what would move and when.
Mullen indicated that some infrastructure, along with residual forces responsible for counterterrorism operations and ongoing training of Iraqi forces, could remain beyond Obama's 16-month timeline.
"In the last several months, he said, military officials have looked at "the totality of what we have there and what would it take to move it out. Generally the answer is two to three years."
There are currently 151,000 U.S. troops in Iraq, and 32,000 in Afghanistan, including 14,500 with the NATO-led coalition, and 17,500 who are fighting insurgents and training Afghan forces.
AP Military Writer Robert Burns contributed to this report.