Townsend, who at one point had figured in speculation as to who would head the then-new Department of Homeland Security, was a familiar face, often appearing to argue the administration's position on morning news and Sunday interview shows.
When Democratic Sen. Russ Feingold called on Bush to refrain from using the phrase ''Islamic fascists'' on grounds it was offensive to Muslims, Townsend explained the president's use of the phrase.
''What the president was trying to capture was this idea of using violence to achieve ideological ends -- and that's wrong,'' Townsend said at a news conference. ''Regardless of what label you pin on it, it is this form of radical extremism that really wants to deny people freedom and impose a totalitarian vision of society on everyone, that we object to.''
She had a high profile in the administration's recent response to the devastating wild fires in California, defending the White House reaction to the disaster as going ''exactly the way it should be'' and assuring Californians the federal response would be ''better and faster'' than its performance in the wake of Hurricane Katrina's strike against the Gulf Coast states in 2005.
''This is not the end of federal assistance. It's just the beginning,'' Townsend said in connection with the wild fires.
Bush noted in his statement that Townsend prosecuted violent crimes, narcotics offenses, Mafia cases and white-collar fraud as an assistant district attorney in Brooklyn, N.Y. and as an assistant U.S. attorney in Manhattan.
No reason was cited for Townsend's departure, and there was no word on a successor.