Frantic authorities escalated efforts to empty this submerged city Wednesday, with the mayor saying that as many as 100,000 people still needed to be evacuated and federal officials readying plans to transport as many as 23,000 refugees of Hurricane Katrina from the Superdome to Houston's Astrodome.

The city grew even more desperate as thousands fled on foot, hundreds of residents clambered onto rooftops to escape floodwaters, and looters plundered abandoned stores for food, liquor and guns. Things have spiraled so out of control, that the city's mayor told the Associated Press that he has ordered police officers to focus on looters and give up search-and-rescue efforts. He also warned that hundreds if not thousands of residents could be dead.

People who had resisted previous evacuation orders, including many elderly and infirm residents, lined up on highways and perched on islands of dry ground waiting for help. They were flown to safety in airborne baskets, ferried in boats or floated in bright-orange plastic buckets, one at a time.

The escalating crisis in New Orleans and along the hard-hit Gulf Coast prompted a surge of activity from the federal government, which dispatched Navy ships to assist in rescue efforts and declared a public health emergency for the region. President Bush, surveying the hurricane- and flood-ravaged area from the air earlier in the day, ordered a coordinated recovery effort for Louisiana, Mississippi and Alabama.

But most of the attention Wednesday was focused on the historic and storied city of New Orleans, which had escaped the worst of Katrina's direct onslaught on Monday, only to be inundated by floodwaters that overwhelmed its extensive system of protective levees and pumps.

Local and federal officials estimated that it could take at least a month to drain all the water that has flowed into the bowl-shaped city, while Mayor Ray Nagin said residents might not be able to return for as long as 16 weeks. Nagin also warned that the city's death toll -- which has been impossible to tally so far -- could be catastrophic.

"We know there is a significant number of dead bodies in the water" along with others who have died while trapped in their attics, Nagin told the Associated Press. When asked how many, he said: "Minimum, hundreds. Most likely, thousands."

Other officials from the state and federal government urged caution in trying to estimate the number killed.

Nagin also estimated that 50,000 to 100,000 people stayed in the city of 485,000 despite earlier evacuation orders, and said they would now be evacuated at the rate of 14,000 to 15,000 a day. He said the city would "not be functional" for about three months.

"It will probably be the largest disaster in the history of the country," Sen. Mary Landrieu (D-La.) said in Baton Rouge, the drier Louisiana city serving as the central staging ground for New Orleans rescue efforts. "Right now every asset is being brought to bear."

Authorities said floodwaters had leveled off or even began receding in some neighborhoods Wednesday. But the Superdome, which has served for days as a dark and dreary shelter for about 23,000 refugees, was surrounded by several feet of water that showed little evidence of dropping late in the day.

The flooding slowed plans announced by state and federal officials Wednesday morning to move the Superdome inhabitants 350 miles west to another stadium, the Astrodome. Millions in the region also remained without power, while hundreds of roads were impassable because of collapse or flooding.

Russ Gilbert, waiting at a Chevron station west of town that has become a gathering place for refugees, said he had to leave his 75-year-old mother because she was unwilling to leave their three-story house near Tulane University.

"The water started coming in the sewer pipes last night," Gilbert said. "It seeped through the drain pipes and began filling up the street. By 7 a.m. it was coming up the curb and then flooded the car. We had to dry the carburetor." By 8 a.m., he said, the water was lapping into the house.

At a news conference, Louisiana Gov. Kathleen Babineaux Blanco tersely rejected suggestions that authorities had not moved aggressively enough to evacuate the city: "We begged all those people to get out," Blanco said. "Even those with limited circumstances were given the opportunity" to leave.

Blanco also said she was "furious" about chronic looting in New Orleans. "This is intolerable," she said.

Perhaps the only piece of good news came with regard to the water level, which authorities said was finally leveling off and decreasing as swollen Lake Pontchartrain slowly emptied into the sea. But until two major breaches on the 17th Street and London Avenue canals can be patched, local and federal authorities said, it would be impossible to empty much of the city with repaired pumps or replacements.

The U.S. Army Corps of Engineers, unable to reach the breaches by land or sea, resorted to announcing a dramatic plan to drop highway barriers, gravel and bags of sand weighing as much as 20,000 pounds from military helicopters in an attempt to close the gaps. But as of late Wednesday, the plan had not been implemented.

Army Corps officials also said Wednesday that they planned to purposely breach levees in two areas outside Orleans Parish to help empty some of the flooded areas.

Walter Baumy, chief of the Army Corps engineering division in New Orleans, told reporters in a conference call that authorities could not have been prepared for the scale of Katrina and the severity of the aftermath.

"There was a plan in place," Baumy said. "It was much more than envisioned. The city has never seen anything like this."

The refugees, meanwhile, continued to flee the city by the thousands. Among those traveling west were two patients from East Jefferson Hospital in Metairie, who were discharged to make way for flood victims.

One of the patients, Kathy Reichert, spoke through tears as she described the damage Katrina inflicted. Nine of her extended family's 10 houses had been destroyed, she said. She was hitching a lift to Lake Charles.

Still others were headed the other way, into New Orleans, attempting to evade roadblocks and other barriers in a frantic search for loved ones. Nick Marks traveled from Santa Monica, Calif., and is trying to reach his father, who is trapped in an area flooded with about 15 feet of water.

"He's really elderly and sick, and I'm just trying to get to him," Marks said. "I've been up for 40 hours."

Another refugee, Sarah Hall, said her house just outside the French Quarter was destroyed in the flooding. Hall said she had been staying at a Sheraton in the city and was heading for another hotel in Baton Rouge.

"Where we lived it was over the sidewalk, a foot, foot and a half deep," she said. "Yesterday it wasn't covering the sidewalk. Overnight it moved two blocks."

One of the most unusual rescue efforts Wednesday happened at Orleans Parish prison, where flooding and sanitation problems led officials to begin evacuating the facility. As of late Wednesday, nearly half of the 5,100 prisoners had been moved to other jails, officials said.

The inmates "haven't eaten for two days and they're not very happy people," Pam Laborde, a representative for the Louisiana Department of Public Safety and Corrections, said before the evacuation operation began. "And we're not dealing with any Boy Scouts here."

Authorities said a troopship, the USS Bataan, was dispatched to New Orleans to provide communications and medical facilities. Mortuary teams have also been sent to try to retrieve dead bodies, said Mark Smith, spokesman for the Louisiana Office of Homeland Security and Emergency Preparedness.

While authorities in Houston readied the mothballed Astrodome for an influx of refugees, thousands of others were already streaming into Baton Rouge, about 90 miles north of New Orleans. To the surprise of Red Cross officials, for example, five busloads of Superdome evacuees showed up Wednesday afternoon and were placed in the capital city's River Center complex along the Mississippi River. With as many as 100,000 refugees already placed in shelters across the region, refugees must travel increasingly long distances for accommodations, emergency management officials said. In Alexandria, a city of 50,000 residents about 150 miles northwest of New Orleans, about 6,000 refugees are being housed, and officials have been told to expect up to 30,000 more. "That's half the city," said City Council member Roosevelt Johnson.

Construction worker Michael Roberts, 43, was already hitting the streets looking for work after settling into a shelter Wednesday in Alexandria. After all, he said, "we might be living here."

Eggen reported from Washington. Staff writers Ann Gerhart and Peter Slevin in New Orleans, Jacqui Salmon and Peter Whoriskey in Baton Rouge, and Christopher Lee in Biloxi, Miss., contributed to this report.

David Johnson, who was unable to walk, is carried from his home in eastern New Orleans by Mickey Monceaux. Authorities say the water is leveling off as Lake Pontchartrain empties in the Gulf.Estelle Dowl and daughter Cayla follow son Nathaniel toward the Louisiana Superdome. The 23,000 people at the emergency shelter are to be moved by bus convoy to Houston.Candice Victor, who said she was in labor, is helped to a vehicle by her husband, Janiero, right, and an unidentified man. The USS Bataan, a troopship, was dispatched to the region to provide medical facilities.