Tens of thousands of people in New Orleans were trapped in rising floodwater, even though hundreds of buses, trains and planes could have brought them to safety before Katrina struck the US Gulf Coast of August 29.

Nightmarish acts of violence took place over several days among evacuees huddled in the city's Superdome and looters roamed downtown unchecked, as the most powerful and well-equipped military in the world remained on stand-by.

And in the world's richest economy, survivors pleaded for water, food and baby milk that could have easily been dropped in by helicopter.

"Confusion reigned at every level of government," The Washington Post said on Sunday in a damning probe into what wrong.

"Compounding the natural catastrophe was a man-made one: the inability of the federal, state and local governments to work together in the face of a disaster long foretold."

Part of the reason for this is historic.

The US constitution carefully limits the power of the federal government to intervene in the affairs of state: the central government cannot simply wade in and take control. And, at state level, a state constitution spells out the division of authority between the governor and at local level.

These principles are cherished and well-tested safeguards of devolved government and individual freedom.

But, when Katrina hit, these multiple layers of government -- each with their fiefdoms of power and with relief plans that were poorly integrated, if at all, with the others' -- helped lay down a fog of confusion.

"When the rubber met the road, it didn't work," said Philip Joyce, professor of public policy and public administration at George Washington University in Washington, D.C.

The Pentagon has been keen to ward off criticism that it had been slow or indifferent to the burgeoning crisis in New Orleans, or that its actions had been hogtied by bureaucracy.

"A lot of folks are saying, 'Well, why did it take so long?'" Department of Defense spokesman Major Paul Swiergosz, said on September 2.

"There are a lot of processes that have to take place, and they are not bureaucratic processes either," he said.

State governors have powers to mobilise their state National Guard, and to bring in reinforcements from other states in a crisis.

But the US military is prevented by law from acting in a domestic law-enforcement role unless authorised by the president, and this is an act of extreme rarity.

In its Sunday report, The Washington Post said that on Thursday, September 1, Bush planned to demand that Louisiana Governor Kathleen Blanco hand over control of her National Guard troops in order to take control of the relief effort.

This idea was hashed out further at a White House meeting early the following day, in talks between Bush, his generals, Vice President Dick Cheney and Michael Chertoff, head of the Department of Homeland Security. But it was never implemented.

But the confusion was not just a problem of coordination within the vertical layers of federal-state-local government.

Within the different branches of the federal government, poor communication gave decision-makers an early impression that New Orleans had "dodged" Katrina's bullet -- and it took several days for this misapprehension to clear and realise just how bad the flooding was.

By general consensus, Chertoff's sprawling department flunked in its first test since it was created in the wake of 9/11.

Its disaster troubleshooter, the Federal Emergency Management Agency (FEMA), is not supposed to be a "first responder" -- it has to wait for an invitation in order to act.

But local officials in New Orleans and Louisiana state officials say they made innumerable appeals for help, and often waited in vain for a response. FEMA's boss, Michael Brown, quit on Monday.

Joyce said a dissection of FEMA's problems could reveal that the agency had suffered at being placed under the helm of a political appointee rather than a professional, and at losing its cabinet-level status and direct line to the president when it was taken over by the Department of Homeland Security in

In the past four years, funding for FEMA's disaster-relief missions had been cut and experienced personnel quit in droves.

"If you're spending time worrying about the next terrorist attacks, maybe you're not worrying enough about the next hurricane strike," Joyce said in an interview with AFP.

He predicted that the Katrina debacle would not necessarily swing the political pendulum towards the creation of a "stronger" central government that would weaken local and state authority.

But, he said, it might breed support for stronger federal government spending when it came to disaster preparedness, making more money available for preparation and coordination.

"A lot of people have been convinced that you can have government without having to pay for it" and this could change, he predicted.