A makeshift tomb at a New Orleans street corner conceals a body that had been lying on the sidewalk for days in the wake of Hurricane Katrina

Homeland Security Secretary Michael Chertoff is warning Americans to be prepared for what he calls an 'ugly scene' in the wake of Hurricane Katrina. The secretary's comments referred to the flooded city of New Orleans, where receding waters are revealing corpses of victims, which officials say could number in the thousands.

Speaking on Fox News Sunday, Homeland Security Secretary Michael Chertoff said there will be more grisly signs of Katrina's devastation in the days to come. "I think we need to prepare the country for what's coming. What's going to happen when we de-water and remove the water from New Orleans is, we are going to uncover people who have died, maybe hiding in houses, got caught by the flood, people whose remains are going to be found in the streets. There is going to be pollution. It is going to be about as ugly a scene as you can imagine," he said.

Tens-of-thousands of survivors have been evacuated from New Orleans to other parts of the country. But, in the meantime, the exact number of dead will not be known for some time. Officials estimate hundreds, maybe thousands of deaths, mostly people who were killed by the storm, or who succumbed while waiting to be rescued.

One of the luckier survivors was Bobby Lane. He and his family had tried to ride out the storm in a neighbor's attic. "We looked out the ventilation of the attic, and we saw the water about a foot from the attic. Man, the women asked, what was going on? So, we had to lie to them and tell them something different. You know what I'm saying? We didn't want to get them upset. It was a horrible sight, I'll tell you that," he said.

This was the type of situation also described by Senator Mary Landrieu, a Democrat from Louisiana, who said she feared many more people drowned in their homes.

While touring some of the hardest-hit areas for the ABC television program This Week, she emphasized the area's importance to the United States. "We supply the seafood, we supply the oil, we supply their goods through our ports. We're proud of it, we are a proud people, and we're good people. But their infrastructure, our infrastructure, is devastated. Their lives are in shatters. The region is torn to pieces," she said.

The last 300 evacuees left New Orleans Superdome Saturday night. The facility had housed some 20,000 hurricane survivors.

On Sunday, power companies planned to send trucks into the city to assess storm damage. National Guard troops would escort the utility vehicles.

The Bush administration has come under sharp criticism from New Orleans residents, among others, for not responding effectively to the hurricane disaster quickly enough.

Secretary Chertoff defended the federal government in an answer Sunday to reporters. "There will be plenty of time to do 'lessons learned.' From this point on, I only have one thing I want to think about, which is making sure we are doing everything possible, as quickly as possible, to prevent misfortune and loss of life and distress. And I'm not going to take one minute away from that to answer questions about things, which we will have plenty of time to revisit later," he said.

After nearly a week of chaos following last Monday's storm, Mr. Chertoff said the federal government is now in control of New Orleans.

President Bush toured the region Friday, and is expected to return within days. On Sunday, he spoke from the headquarters of the American Red Cross. "The world saw this tidal wave of disaster descend upon the Gulf Coast, and now they're going to see a tidal wave of compassion," he said.

He said this "tidal wave of compassion" included 5,000 Red Cross volunteers who were working at shelters in 19 states, which have accepted evacuees.

Meanwhile, other top U.S. officials also have been dispatched to the region, including Secretary of State Condoleezza Rice and Defense Secretary Donald Rumsfeld.