"Katrina exposed serious problems in our response capability at all levels of government," Mr. Bush said at joint White House news conference with the president of Iraq. "And to the extent that the federal government didn't fully do its job right, I take responsibility."
More grim news came Tuesday, as Hurricane Katrina's death toll in Louisiana climbed to 423 Tuesday, up from 279 a day before, the state Health Department said.
The jump came as recovery workers turned more and more of their attention to gathering up and counting the corpses in a city all but cleared out of the living.
How high the death toll might go is unclear.
Mayor Ray Nagin said earlier this month that Louisiana could have 10,000 dead. But a street-by-street sweep of the city last week yielded far fewer bodies than feared, and authorities said the death toll could be well below the dire projections.
Up until the past few days, authorities were slow to release numbers, saying they were concentrating on rescuing the living first. Rescuers reported pushing corpses aside, or tying them down to banisters or roofs for workers to collect later.
In other developments:
Mr. Bush's admission comes just days after accusing the news media and critics of the administration storm response of "playing the blame game," reports CBS News White House Correspondent Peter Maer.
"I want to know what went right and what went wrong," the president said. "I want to know how to better cooperate with state and local government, to be able to answer that very question that you asked, 'Are we capable of dealing with a severe attack or another severe storm?'"
Homeland Security Secretary Michael Chertoff said the relief operation was entering a new phase.
Initially, he said, the most important priority was evacuating people, getting them to safety, providing food, water and medical care.
"Now we have to reconstitute the communities that have been devastated," Chertoff added.
He said the federal government would look increasingly to state and local officials for guidance on rebuilding the devastated communities along the Gulf Coast.
"The federal government can't drive permanent solutions down the throats of state and local officials," Chertoff said. "I don't think anyone should envision a situation in which they're going to take a back seat. They're going to take a front seat," he said.
Chertoff said that teams of federal auditors were being dispatched to the stricken areas to make sure that billions of dollars worth of government contracts were being properly spent.