"In leading the policy process on issues such as taxes, entitlements, healthcare, energy security, the environment and trade and investment, Al contributed his own ideas and also worked to ensure that all views were brought to the table and given fair analysis and debate," Bush said in a statement. "He brought to the White House his capacity for hard work and creative thinking and fostered an open, cooperative working environment."

Bush named NEC deputy Keith Hennessey as Hubbard's successor. Hennessey has been a deputy to three NEC directors and worked for Sen. Trent Lott, R-Miss., on the Senate Budget Committee.

Hubbard joined the administration following Bush's 2004 re-election.

Last week Homeland Security Adviser Frances Townsend resigned and Bush has also lost chief political adviser Karl Rove; communications chief Dan Bartlett; and budget director Rob Portman in the past six months.

Such high-profile staff changes are usual as an administration heads into its final year.