Fleischer wants to "dismantle
live nuclear weapons"
Fleischer, who got married six months ago, said the 11 September attacks and wars in Afghanistan and Iraq had taken their toll on him.
The White House spokesman said he would help Bush in his re-election campaign before moving back to New York.
No replacement was announced but speculation centred on Victoria Clarke, the Pentagon spokeswoman who regularly briefed the press during the US-led war against Iraq.
Deputy Press Secretary Scott McClellan was also seen as a replacement.
Fleischer said a key motive for resigning now was to spend more time with his wife.
The White House spokesman enjoys a close relationship with Bush although he is not from the President’s band of Texas advisers.
Fleischer’s role exploded in the aftermath of the 11 September attacks when all-news television networks broadcast his entire daily briefings.
He sometimes privately rebuked journalists by telephone.
Fleischer’s career was not without its low points. He denied that Bush would hold a mid-March summit in the Azores with British Prime Minister Tony Blair and Spanish Prime Minister Jose Marie Aznar a day before it was announced.
He admitted making a mistake after saying “one bullet” shot at former Iraqi President Saddam Hussein would be less expensive than a war.
Fleischer also came under fire for blaming Middle East violence on what he described as former US President Bill Clinton’s over-ambitious “attempt to shoot the moon and get nothing” in the region.
On 26 September 2001 he said Americans “need to watch what they say, watch what they do”, even after Bush said civil liberties would not be affected in Washington’s “war on terror”.