All levels of the US government, from President Bush down, were at fault for the poor response to Hurricane Katrina, a leaked Congressional report says.
The authorities were mocked in a weekend parade in New Orleans
Homeland Security Secretary Michael Chertoff is singled out for particular criticism in the document, which is due to be published on Wednesday.
Overall, it says, the government's response was marked by "fecklessness, flailing and organisational paralysis".
The report, leaked to the US media, is one of several into the disaster.
Entitled "A Failure of Initiative", the 600-page document suggests something approaching a national disgrace, says the BBC's Justin Webb in Washington.
Produced by a special Republican-dominated House inquiry, it issues 90 separate findings.
"Our investigation revealed that Katrina was a national failure, an abdication of the most solemn obligation to provide for the common welfare," says the report's summary, seen by the Associated Press.
"At every level - individual, corporate, philanthropic and governmental - we failed to meet the challenge that was Katrina."
According to reports, the document concludes:
- Michael Chertoff implemented the emergency response systems "late, ineffectively or not at all", which delayed federal troops and supplies by as much as three days
- White House staff were unable to effectively "substantiate, analyse and act on the information at its disposal", giving President Bush poor and incomplete counsel
- Late decisions to issue mandatory evacuations by New Orleans Mayor Ray Nagin and Louisiana Governor Kathleen Blanco led to deaths and prolonged suffering
- The Federal Emergency Management Agency (Fema) suffered from a lack of trained and experienced personnel.
"If 9/11 was a failure of imagination, then Katrina was a failure of initiative," the report's summary states.
"In this instance, blinding lack of situational awareness and disjointed decision-making needlessly compounded and prolonged Katrina's horror."
'Path to failure'
The investigators said they "are left scratching our heads at the range of clumsiness and ineptitude that characterised government behaviour before and after this storm.
"If this is what happens when we have advance warning, we shudder to imagine the consequences when we do not."
President Bush, after a relatively strong start to this year, is suddenly faced by an immense political challenge with this report, our correspondent says.
Hurricane Katrina was one the worst natural disasters in US history, killing more than 1,300 people across five states when it hit last August. Hundreds of thousands of people were displaced in its aftermath.
Ex-Fema boss Michael Brown has contradicted official accounts
On Friday, Michael Brown - who quit as Fema chief after the disaster - told a Senate oversight panel that officials knew levees were breached in New Orleans much earlier than admitted but did not act swiftly enough.
He also criticised the Department of Homeland Security, which controls Fema, saying its policies had put his organisation on "a path to failure".
Mr Brown argued that the response to Hurricane Katrina would have been more effective if a terrorist had blown up one of the levees.
Natural disaster, he said, had become the "step-child" in the Department of Homeland Security.