President George W Bush has promised the US government will do and spend whatever it takes to rebuild the hurricane-hit Gulf Coast.
Speaking from New Orleans, Mr Bush said billions of dollars would be spent on the reconstruction - "an unprecedented response to an unprecedented crisis".
New Orleans' Mayor Ray Nagin said three districts would re-open next week, and the French Quarter a week later.
Meanwhile, the confirmed death toll from Hurricane Katrina rose to 792.
The president's prime-time speech from the historic French Quarter came on his fourth trip to the region since Katrina smashed communities across the Gulf Coast more than two weeks ago.
He made the speech the night before places of worship across the US began observing a national day of prayer on Friday for the victims of the hurricane.
Mr Bush made what observers say is one of the most important speeches of his presidency in a deserted Jackson Square, in an empty city, addressing millions of people via the airwaves.
Gulf opportunity zone Immediate incentives for job-creating investment
Recovery accounts Up to $5,000 help for job-seekers, for training, childcare etc
Urban homesteading act Federal-owned land handed out in a lottery for new homebuilding
His approval ratings have slumped to the lowest point of his presidency, with only about 40% of voters expressing confidence in Mr Bush.
Continuing conflict in Iraq and rising fuel prices were affecting his support even before Hurricane Katrina struck.
The BBC's Justin Webb, in Washington, says the content of the speech will have surprised some of his own supporters, but pleased a lot of Americans.
"Throughout the area hit by the hurricane, we will do what it takes. We will stay as long as it takes to help citizens rebuild their communities and their lives," Mr Bush said.
"There is no way to imagine America without New Orleans, and this great city will rise again."
The president acknowledged that his government had not dealt adequately with the aftermath of Hurricane Katrina, which devastated a vast area on the US southern coast.
He said he had ordered every cabinet member to take part in a review of procedures.
"It was not a normal hurricane, and the normal disaster relief system was not equal to it," he said.
He ordered the Department of Homeland Security to initiate an immediate review of emergency plans in every major city in the US.
Congress had cleared $60bn (£33bn) of funds to be spent on the reconstruction effort, he said, and more would be forthcoming.
The floods left houses full of mud and mould
He announced new initiatives to help the Gulf Coast back to its feet, including incentives for business investment to encourage new jobs, financial help for job-seekers, and a lottery dishing out government land on which "urban homesteaders" could build.
Mr Bush said poverty had played its part in the damage wrought by the storm, and called for national unity.
He said the rebuilding of the stricken area would be a "great national enterprise" and urged Americans all over the country to "find their role and do their part".
Our correspondent described the speech as a fight back at a political level, but said some of it would be quite shocking to conservative Americans.
The entire speech was one that Bill Clinton could have given, he added.
Mayor Nagin earlier announced that residents would be allowed to return to some parts of the city from next week, allowing about a third of its 485,000 people back home.
"The city of New Orleans will start to breathe again," he said.
Mayor Nagin said the first section to re-open to residents would be Algiers on Monday. The city's uptown areas would follow in stages next Wednesday and Friday.
However, much of New Orleans still lacks basic amenities such as clean water and electricity, Claire Marshall reports from the city.
It is thought that around 40% of the city is still rotting under the fetid flood waters, our correspondent says.
People are being advised that the receding flood waters contain hazardous substances, such as E. coli, lead and arsenic.