In a prime time speech addressing the American people on the aftermath of Katrina, Bush said on Thursday: "Four years after the frightening experience of September 11th, Americans have every right to expect a more effective response in a time of emergency.
"When the federal government fails to meet such an obligation, I as President am responsible for the problem, and for the solution," he said.
His speech came as the toll from Katrina was put at almost 800 people dead and one million displaced in the US Gulf Coast region.
Washington's response, widely criticised as sluggish and timid, sent Bush's approval ratings - already battered by the war in Iraq - to their lowest levels, and tarnished his image as a strong leader in a crisis.
"It was not a normal hurricane, and the normal disaster relief system was not equal to it," he said. "The system, at every level of government, was not well coordinated, and was overwhelmed in the first few days."
Review of response
Bush said he had ordered the Department of Homeland Security to review emergency response plans for every major US city and told his Cabinet to study Washington's response.
"I consider detailed emergency planning to be a national security priority," said the president, whose roughly 20-minute speech came after members of his Republican party urged him to get a firmer grip on the public response to the storm.
But he did not endorse calls, mostly from opposition Democrats, for an independent investigation modelled on the commission that probed intelligence failures in the run up to the 11 September, 2001 attacks.
Bush unveiled a package of investment, housing, health care, education and job-promotion for the US Gulf Coast as part of what he said would be "one of the largest reconstruction efforts the world has ever seen."
But he declined to put a price tag on the project, which has already nearly burned through an initial $62 billion and may run into the hundreds of billions - even eclipsing spending on the war in Iraq.
"The system, at every level of government, was not well coordinated, and was overwhelmed in the first few days"
"Our goal is to get the work done quickly," said Bush, who gave an unusually detailed account of the horrors Americans experienced in the first days after Katrina struck and led to flooding in New Orleans.
He referred to "the kind of desperation no citizen of this great and generous Nation should ever have to know: Fellow Americans calling out for food and water, vulnerable people left at the mercy of criminals who had no mercy, and the bodies of the dead lying uncovered and untended in the street."
And he said that Washington must have greater authority and rely more on the US military, "the institution of our government most capable of massive logistical operations on a moments notice."
Before Bush spoke, New Orleans Mayor Ray Nagin said businesses could return to the historic French Quarter, the central business district and the uptown and Algiers neighbourhoods on Saturday, almost three weeks after the storm smashed levees and flooded most of the city.
Residents of those areas, making up about 40% of the city's population, would be allowed to return in the following days in a phased process, he said.
Nagin wants businesses to start
returning to New Orleans
"It is a good day in New Orleans," Nagin said. "We're bringing New Orleans back."
Many other neighbourhoods could take months to reopen. Some will probably have to be levelled but perhaps half the homes in the city of 450,000 people could be salvaged, Nagin said.
Bush, who has rejected accusations that he acted slowly in response to Katrina because the storm's hardest-hit were poor and black, said the reconstruction should tackle the "deep, persistent poverty in this region."
"That poverty has roots in a history of racial discrimination, which cut off generations from the opportunity of America. We have a duty to confront this poverty with bold action," he said.
Massachusetts Democratic Senator John Kerry, who lost the presidential race to Bush last year, was dismissive.
"Leadership isn't a speech or a toll-free number. Leadership is getting the job done. No American doubts that New Orleans will rise again, they doubt the competence and commitment of this administration," Kerry said.