White House National Security Adviser Gen James Jones is stepping down. He will be replaced by his deputy, Tom Donilon.
President Barack Obama announced the changes at the White House on Friday.
The BBC reports the announcement had been widely expected. Several other senior White House advisers are departing, including economic adviser Larry Summers who is to return to Harvard University.
General Jones, a former Marine Corps general, is the first high-level member of Mr Obama's national security team to depart.
A recent book by veteran reporter Bob Woodward of The Washington Post quoted Defence Secretary Robert Gates as saying Mr Donilon would be "a disaster" as a national security adviser.
However, Mr Gates disavowed that at the Pentagon on Friday.
General Jones retired from the Marine Corps in 2007 after more than 40 years, to take a position as the State Department's special envoy for middle east regional security.
