Federal Emergency Management Agency (Fema) director Mike Brown said on Monday he was stepping down "in the best interest of the agency and best interest of the president".
Brown, under fire for Fema's performance in the Gulf Coast, said he feared he had become a distraction.
"I think it's in the best interest of the agency and the best interest of the president to do that and get the media focused on the good things that are going on, instead of me.
"The focus has got to be on Fema, what the people are trying to do down there," he said.
David Paulison, a former Miami fire chief with 30 years in the emergency services and experience of Florida's devastation in the aftermath of Hurricane Andrew in 1992, was announced as Brown's replacement at the head of the agency.
He was abruptly recalled to Washington on Friday, a clear vote of no confidence from his superiors at the White House and the Department of Homeland Security.
Brown had been roundly criticised for Fema's sluggish response to the hurricane, which has caused a huge political problem for President George Bush, sending his opinion numbers plunging.
He was also accused of padding his resume, a charge he denied on Friday.
"I think it's in the best interest of the agency and the best interest of the president to do that and get the media focused on the good things that are going on, instead of me"
Federal Emergency Management Agency director
The president ducked questions about Brown's resignation.
"Maybe you know something I don't know. I've been working," Bush said on an inspection tour of damage in Gulfport, Mississippi.
Bush said he planned to talk to Brown's boss, Homeland Security Director Michael Chertoff, from Air Force One on the flight to Washington.
"There will be plenty of time to figure out what went right and what went wrong," Bush said.
Brown, who said he last talked to Bush five or six days ago, said the resignation was his idea. He spoke on Saturday to White House chief of staff Andy Card, who did not request his departure, according to Brown.
Also on Monday, Bush refused to identify any specific failures in Washington's response to Katrina and flatly denied that race decided who escaped the killer storm.
"The storm didn't discriminate, and neither will the recovery effort," he said as he got his first close-up look of downtown New Orleans two weeks after Katrina turned the once-proud jazz capital into a fetid swamp.
Some local officials and black leaders have charged that the government dragged its feet in responding to the disaster because most of the people unable or unwilling to flee the drowned city were black.
Bush: Racism and Iraq are not
to blame for Katrina response
Focusing instead on the rescue efforts, Bush said emergency workers "didn't check the colour of a person's skin" before pulling them to safety and vowed: "The rescue efforts were comprehensive and recovery will be comprehensive."
The president toured storm-ravaged sections of New Orleans, then met officials of St Bernard's Parish - just east of New Orleans and one of the worst hit areas - who have been critical of the federal response to the catastrophe.
Bush, who also met emergency personnel and troops, angrily rejected any suggestion that National Guard deployments in Iraq had in any way hampered the early response to Katrina.
"It is preposterous to claim that the engagement in Iraq meant there wasn't enough troops here. It's pure and simple," he said forcefully. "We've got plenty of troops to do both."
But Lieutenant-General Steven Blum, head of the National Guard Bureau, reportedly said last week that "arguably" one day of response time was lost due to Mississippi and Louisiana National Guard deployments in Iraq.
"It is preposterous to claim that the engagement in Iraq meant there wasn't enough troops here. It's pure and simple. We've got plenty of troops to do both"
US President George Bush
"Had that brigade been at home and not in Iraq, their expertise and capabilities could have been brought to bear," he was quoted as saying.
Bush also sought to clarify his comment that no one had anticipated that New Orleans' levees would break, which came despite government warnings and alarms sounded in the media on precisely that issue.
"What I was referring to is this: When that storm came by, a lot of people said we dodged a bullet," he said.
"And I myself thought we had dodged a bullet. You know why?
Because I was listening to people probably over the airwaves say 'the bullet has been dodged'. And that was what I was referring to," he said.
Bush, making his third visit to the battered US Gulf Coast, has
sought to counter widespread attacks on Washington's Katrina
response with photo-opportunities even as he faces his worst-ever poll numbers.
Polls show most Americans believe Bush could have done more to help Katrina's victims, although they also blame leaders of Louisiana and New Orleans.