Hurricane Katrina and the ensuing floods along the Gulf Coast could mark one of the deadliest natural disasters in U.S. history, as the macabre task of locating and cataloguing its dead moves into its early stages. Officials estimate the death toll could rise to several thousand over coming days.

The search-and-rescue efforts in coastal communities of Louisiana and Mississippi are turning their focus to recovering the bodies, as workers attempt to reach isolated communities that were ravaged by high winds and flooding that reached rooftops. The more than 200 confirmed dead suggest a grimmer total, as rescuers break residential windows to find bodies floating in flooded houses, to discover victims under piles of tree limbs, wood planks and rocks, and to secure bodies found floating in the streets to fence posts.

Totals of the dead are elusive, say local, state and federal officials, because of great difficulty finding missing people trapped in nursing homes, office buildings and apartment complexes. Debris is piled more than 10 feet high in Mississippi. In New Orleans, the battle is against deep waters and completely obstructed roadways.

New Orleans Mayor C. Ray Nagin (D) told NBC's "Today" that "it wouldn't be unreasonable to have 10,000" dead as a result of the catastrophe, and Louisiana Gov. Kathleen Babineaux Blanco (D) said thousands were probably killed.

Homeland Security Secretary Michael Chertoff, in Baton Rouge on Monday, warned that the death toll is "going to be an unhappy number."

Should that number reach near the 10,000 mark, Katrina could be remembered as the deadliest natural disaster in U.S. history. The September 1900 hurricane that swamped Galveston, Tex., left more than 8,000 dead. The San Francisco earthquake and fire in 1906 claimed about 3,000 lives.

Mississippi's estimate of the dead is 150, but official death numbers are not released until a coroner has identified the body. In Hancock County, for example, rescue officials believe the announced total of 36 dead could easily rise to between 600 and 1,000. Rescuers there were going from house to house and leaving coded markings to indicate suspected deaths, and then moving on.

"It's access more than anything," said Mick Bullock, a spokesman for the Mississippi Emergency Management Agency, who said there have been reports of people being trapped in their attics for the past week. "There's so much debris still blocking traffic. These local roads are really still covered up, and there are places we haven't been able to get to. . . . It's going to be an extensive and long process. The reality is that the death toll will climb."

Louisiana officials have counted 71 dead so far.

In St. Gabriel, a tiny hamlet south of Baton Rouge, La., the dead may soon outnumber the living.

In a cavernous warehouse, across from the local baseball field in this gritty town of 5,000, the bodies of those killed during Katrina's fury and its deadly aftermath started arriving yesterday.

Plucked from the filthy floodwaters, the bodies will be transported in refrigerated trucks to this temporary morgue. There, they will be washed, examined, photographed, fingerprinted and, eventually, released to their families when they have been identified. Seven refrigerated trucks were lined up to hold bodies for processing.

This morgue, essentially the major clearinghouse for those killed in Louisiana, and a similar facility in Mississippi will take bodies from several regional collection points throughout the affected area. The St. Gabriel mortuary unit is set up to process in excess of 5,000 dead, said Ricardo Zuniga, a FEMA spokesman.

Jeffrey Kraft, publisher of American Funeral Director magazine in Rockville, said the facility was significantly larger than the temporary morgue set up to handle the dead from the Sept. 11, 2001, attacks on the World Trade Center, where more than 2,700 died.

Once bodies are turned over to the smaller collection points, basic identifying information and specific data about where the body was found is noted. Then, the bodies travel under police escort to the larger mortuary units for forensic inspection. After all of that information is processed, the bodies move on to state control for identification and notification of families.

On Monday, before the truckloads of body bags began to arrive in St. Gabriel, federal and state officials briefly opened the facility -- expected to be the main morgue for bodies retrieved west of the Mississippi River -- to journalists before it is closed to anyone except morgue staff.

Officials said they wanted to show families, and the country, the conditions under which the bodies would be handled.

"Families need to know what happened to their loved one," said David Senn, a forensic odontologist who helped identify victims of the Columbia shuttle disaster and the World Trade Center attacks.

Inside the facility, slightly smaller than a football field, sheets of black plastic were taped down to concrete floors. A dozen metal gurneys were already lined up near the loading dock, ready to transport bodies to the blue-and-white decontamination tent. Officials said they will be able to process 140 bodies a day.

FBI fingerprint specialists and teams of volunteer forensic pathologists, forensic odontologists, archaeologists, and DNA experts from FEMA's Disaster Mortuary Operational Response Team and its Disaster Medical Assistance Team will examine the bodies after they have been decontaminated. A veterinary team will separate human from animal remains. One escort will accompany each body through the entire route, Ellis said.

On a tent pole near the start of the grim assembly line was taped a handwritten sign. "Let the dead teach the living," it said. It is, said Ellis, "a dignified, respectful process."

Staff writers Sally Jenkins in Waveland, Miss., and Timothy Dwyer in New Orleans and staff researcher Karl Evanzz in Washington contributed to this report. White reported from Washington.

A man died of a seizure five days ago -- and his dog has stayed by his side ever since -- at a gas station in the Gentilly Woods area of New Orleans.

A truck in Chalmette, La., carries bodies that were recovered after Hurricane Katrina to a temporary morgue.