New Orleans ? The bodies of more than 40 mostly elderly patients were found in a flooded-out hospital in the biggest known cluster of corpses to be discovered so far in hurricane-ravaged New Orleans.

The exact circumstances under which they died were unclear, with at least one hospital official saying Monday that some of the patients had died before the storm, while the others succumbed to causes unrelated to Katrina.

The announcement raises Louisiana’s official death toll to nearly 280.

Despite the devastation and miles of still flooded streets, there were encouraging signs of recovery: Nearly two-thirds of southeastern Louisiana’s water treatment plants were up and running. Louis Armstrong New Orleans International Airport planned to resume limited passenger service today. Forty-one of 174 permanent pumps were in operation, on pace to help drain the still half-flooded city by Oct. 8.

That doesn’t mean a quick return to normalcy for residents or for business owners, who were let back in Monday to assess the damage and begin the slow process of starting over.

The Federal Emergency Management Agency expects to provide temporary housing for 200,000 hurricane victims for up to five years, most in Louisiana. The agency is planning to use trailer homes to create “temporary cities,” some with populations up to 25,000, said Brad Fair, head of the FEMA housing effort.

A guard keeps watch at Memorial Medical Center in New Orleans, where more than 40 bodies were recovered Monday.

“This may not be quite on the scale of building the pyramids, but it’s close,” Fair said. He had no cost estimates.

Insurance experts have doubled to at least $40 billion their estimate of insured losses caused by Katrina. Risk Management Solutions Inc. of Newark, Calif., put the total economic damage at more than $125 billion.

Lawmakers in Washington proposed some tax changes Monday to help the victims get back on their feet, such as letting them tap retirement accounts without penalty and encouraging donations of cash, food and school books.

Former New Orleans Mayor Marc Morial called for a compensation fund for the hurricane victims similar to the fund created for victims of the terrorist attacks of Sept. 11, 2001.

The death toll has also been rising as more bodies are recovered across the region.

At least 40 bodies were found Sunday at the 317-bed Memorial Medical Center, but the exact number was unclear. Bob Johannesen, a spokesman for the state Department of Health and Hospitals, said 45 patients had been found; hospital assistant administrator David Goodson said there were 44, plus three on the grounds.

Also unclear was exactly how the patients died.

Steven Campanini, a spokesman for the hospital’s owner, Tenet Healthcare Corp., said some of the patients were dead before the storm arrived, and none of the deaths resulted from lack of food, water or electricity to power medical equipment. He said many were seriously ill.

Goodson said patients died while waiting to be evacuated over the four days after the hurricane hit, as temperatures inside the hospital reached 106 degrees. “I would suggest that that had a lot to do with” the deaths, he said of the heat.

Police Chief Eddie Compass declined to answer any questions about the bodies, including whether officers received any calls for help from those inside the hospital after it was evacuated.