"The White House is going through a phase of transition -- a change can be helpful," White House Press Secretary Scott McClellan told a press conference with Bush, reported the Washington Post.
"I've given my all, and will continue to do so as we transition to a new press secretary over the next two to three weeks," he added.
"I thank Scott for his service to our country," Bush said.
"It's going to be hard to replace Scott, but nevertheless he's made the decision, and I accept it."
McClellan, 38, has been in the job more than 2-1/2 years and was one of the most visible faces of the administration. There was no immediate word on who would succeed McClellan, one of a group of Texans Bush brought to the White House.
Rove was Bush's most influential adviser and a dominant force in the administration. (Reuters) Karl Rove, Bush's most influential adviser and a dominant force in the administration, also surrendered key policy responsibilities Wednesday.
He will remain Bush's deputy chief of staff but not policy coordinator, a job he assumed a year ago, senior administration officials said. Rove, another Texas insider, will be replaced with Joel Kaplan, currently the deputy White House budget director.
He has been keeping a low profile while still remaining under investigation in a special prosecutor's probe into outing the name of undercover CIA agent Valery Plame.
US Vice President Dick Cheney's former top aide, I. Lewis "Scooter" Libby, has been indicted with perjury and obstruction of justice after an investigation into same case.
Joseph Wilson, a former ambassador to Gabon, maintains that his wife cover was blown to discredit him after he charged that the administration had "twisted" intelligence to invade Iraq.
After a trip to Niger in February 2002, he said claims that Iraq had tried to buy uranium for nuclear bombs, one of Bush's justifications for the war, were ungrounded.
The departure of McClellan and Rove is part of a makeover by new White House Chief of Staff Josh Bolten to help Bush rebound from sagging poll numbers and bolster American confidence in his leadership.
A recent USA Today/CNN/Gallup survey found that Bush's rating has fallen back to 32 percent over the Iraq limbo.