A key issue that will immediately face the new Defense Secretary will be managing the US withdrawal from Afghanistan.
Afghan President Hamid Karzai is visiting Washington this week for talks on the future of his country once the US and NATO pull out most of their troops by the end of 2014.
But the shape and speed of that draw-down, and what comes next, has yet to be decided.
Adam Entous, national security correspondent for the Wall Street Journal, says the White House is signaling a rapid draw-down to a very low level of troops after 2014.
Chuck Hagel, if confirmed as the new Defense Secretary, will likely be a willing enforcer for the White House's policy of a rapid withdrawal, says Entous.
The army's commander, General John Allen, is asking for a slower withdrawal, and the retention of more troops for the post-2014 scenario.
Karzai, says Entous, is seeking reassurances that his country will not be abandoned.