The bleak assessment will deepen the biggest crisis faced by President George Bush, who last week called the devastation of Hurricane Katrina a "temporary disruption".
As the relief effort finally got under way yesterday for the tens of thousands of people left without food, water, medicines or the rule of law for five days, the federal official in charge of disaster recovery told foreign diplomats that reconstruction cannot begin until next summer.
The President is now facing a political hurricane of his own, with gathering criticism, even from inside his own party, for failing to heed warnings of the city's vulnerability, cutting spending on its defences to pay for the wars on terror and in Iraq, and responding sluggishly to the worst natural catastrophe ever to hit his country.
Ray Nagin, the Mayor of New Orleans, said that every day of delay has caused hundreds of deaths. Louisiana's junior Senator, Republican David Vitter, gave the Bush administration "an F grade" for its handling of the crisis. Senator Chuck Hagel, a leading contender for his party's nomination to succeed Mr Bush, said, "There must be some accountability."
The criticism is all the sharper because the President did nothing to alter his holiday schedule for 48 hours. Vice-President Dick Cheney remains on holiday in Wyoming. Condoleezza Rice, the Secretary of State, returned to Washington after being seen shopping for $7,000 shoes in Manhattan as New Orleans went under.
Dan Craig, the director of recovery at the Federal Emergency Management Agency, told the diplomats that it could take up to six months to drain the flood waters out of New Orleans, and another three to allow the city to dry out. Even then, he added, debris and other hazardous material would need to be cleared away before rebuilding could begin. Evacuees could have to be housed by the government for two years.
Officials said that the job of recovering, let alone counting, the dead may not start for weeks. The death toll is likely to far exceed the numbers killed in the 11 September attacks almost exactly four years ago. Sergeant Nicholas Stahl of the Louisiana Office of Homeland Security and Emergency Preparedness said that rescuers are focusing on finding an estimated 50,000 people still stranded by the flood waters and admitted "there is no system to collect and store bodies".
Even when the bodies are recovered, experts say it will be far harder to identify them than at the World Trade Center, because they are decomposing rapidly in the heat.
Although a government exercise last year predicted the course of the disaster, Mr Bush drastically cut back spending on city defences. Work on strengthening vital levees needed to keep out flood water stopped for the first time in 37 years.Reuse content