WASHINGTON President-elect Barack Obama will quickly face big decisions on the wars in Iraq and Afghanistan as the United States undergoes its first wartime change of administration since the Vietnam era.
The commander-in-chief of the world's only military superpower will also have to grapple with other major national security issues, such as Iran's nuclear program and militancy and instability in nuclear-armed Pakistan.
Faced with such a major transition at such a sensitive time, the Pentagon says it has made unprecedented efforts to ensure a smooth handover to the next administration.
"This is the first wartime transition since 1968, the Johnson-Nixon turnover during the Vietnam War," Pentagon spokesman Bryan Whitman said on Tuesday.
"We are ready to start briefing the incoming administration immediately."
Top of Obama's agenda will be the question of how to juggle the demands of the wars in Iraq, where the United States has more than 150,000 troops, and Afghanistan, where there are more than 30,000 U.S. military personnel.
Obama opposed the Iraq war, which became deeply unpopular as violence and U.S. casualties rose, before it began in 2003. He has pledged a timetable for the withdrawal of U.S. forces that he has suggested could be completed within 16 months.
But top military officers, including Navy Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, and Army Gen. David Petraeus, the high-profile head of U.S. Central Command, have both stated publicly that they oppose a timetable.
They want any withdrawals from Iraq to based on security assessments by commanders on the ground.
ROOM FOR MANEUVER
Both Obama and the military have some room for maneuver. Obama has stressed that he will end the war responsibly, take advice from commanders and not make any precipitous moves.
Similarly, sharp falls in violence in Iraq mean commanders can recommend troop cuts based on security conditions.
And a draft pact between Iraq and the United States, backed by top commanders, sets out targets for troop withdrawals, although they are not as ambitious as Obama has proposed.
Commanders still advocate a cautious approach to withdrawals, fearful that Iraq could once again be engulfed in violence, and Obama will have to decide how hard he is willing to push them to take more risks.
That decision is all the more important because Obama has pledged to send more forces to Afghanistan, where insurgent violence is on the rise, and top military officers say that can only happen if the United States cuts troops in Iraq.
A U.S. Army brigade -- likely more than 4,000 troops once support units are included -- is due to head to Afghanistan early next year but U.S. commanders want three more to step up the fight against Taliban militants and other insurgents.
More broadly, Obama and his top officials will have to evaluate a slew of reviews on Afghanistan strategy ordered in the final months of the Bush administration and decide whether some fundamental changes in approach are required.
The Afghan government has showed a renewed interest in reconciliation efforts with the Taliban. Obama's administration will have to decide how much that is worth supporting.
The border region straddling Afghanistan and Pakistan, where al Qaeda leader Osama bin Laden is believed to be hiding, is an area of major concern to the United States.
Obama will have to consider whether to continue missile strikes on suspected militants by pilotless U.S. aircraft. Those strikes have triggered protests in Pakistan, although some experts say Pakistani officials tacitly back them.
Obama may also face a decision on whether to approve U.S. strikes -- or support Israeli military action -- against Iran if Tehran is believed to be close to enriching enough uranium to produce a nuclear bomb. Obama has said he wants to reach a diplomatic solution if possible.
(Editing by Kristin Roberts and David Storey)