Officials say that about 100,000 of the 500,000 residents of New Orleans live on or below the poverty line, or are elderly and sick, mostly in African-American neighbourhoods. But after years of anticipating a hurricane, officials in effect ignored that this “low-mobility” population would have neither the money nor the transport to flee.

Brian Wolshon, a former consultant on the state’s evacuation plan, told The New York Times that at disaster planning meetings, whenever the question was raised about how to evacuate the poor and infirm, “the answer was often silence”.

Experts also listed other crucial errors made before Hurricane Katrina hit and expressed bafflement over how the most anticipated natural disaster in US history brought such a slow and chaotic response. Despite dozens of plans and models over decades predicting a big hurricane hit, including one last year that predicted 10ft to 15ft of water in New Orleans and the evacuation of one million people, local, state and federal officials have been overwhelmed by the disaster.

Several experts said yesterday that a crucial error may have been the failure to predict that the levees holding back Lake Pontchartrain would be breached. It was an omission that appeared extraordinary given the parlous state of the defensive walls and the near certain belief among federal and state officials for years that in the aftermath of a hurricane, New Orleans would be flooded.

Eric Tolbert, a former senior official in the Federal Emer-gency Management Agency (Fema), said that after the Asian tsunami last year: “New Orleans was the No 1 disaster we were talking about. We were obsessed with New Orleans because of the risk.”

Martha Madden, a former secretary of the Louisiana Department of Environmental Quality, said that it was incomprehensible that immediate federal help, particularly troops on the ground, had not been provided. She said: “They can’t drop some food on Canal Street in New Orleans right now? It’s mind-boggling.”

In 2000 and last year, disaster plans were prepared for a significant hurricane hit, but officials say that nobody thought that the levees would be holed. Greg Breerwood, of the US Army Corps of Engineers, which is responsible for maintaining the levee system, said: “We knew . . . some levees and flood walls would be overtopped. We never did think they would be breached.”

Budget cuts to the city’s defences by successive administrations in Washington compounded the problem. Last year the army engineers sought $105 million (£57 million) for hurricane and flood programmes in New Orleans. The White House slashed the request to $40 million and Congress approved $42.5 million. Mr Tolbert said that funding dried up after the hurricane exercise last year, leading to the shelving of plans to shelter survivors. Last year Al Naomi, the head of the army engineers in New Orleans, complained that federal budget cuts had halted work on the city’s east-bank levees for the first time in 37 years.

Analysts expressed amazement that despite Hurricane Katrina’s slow approach from the Gulf of Mexico, large numbers of National Guardsmen were not in place before it made landfall, and that it took until yesterday, four days after the disaster, for troops to arrive.

Charles Boustany Jr, a Republican Louisiana congressman, said that he spent 48 hours after the hurricane calling the White House to impress upon Mr Bush the scale of the crisis.

Terry Ebbert, the chief Homeland Security official in New Orleans, said: “This is a national disgrace. Fema has been here three days, and we have no command and control. We can send massive amounts of aid to tsunami victims, but we can’t bail out the city of New Orleans.”

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