Amos Cormier, chairman of the Plaquemines Parish Council, said he saw no sign of the Federal Emergency Management Agency, or the National Guard until Saturday. He said the National Guard had been requested Wednesday.

Troops were moving into the Mississippi coast, bringing water and ice, helping to keep order, said Stacey Morrison of the Mississippi Emergency Management Agency. She said the American Red Cross had set up more than 100 shelters in the state.

Conditions in some of the shelters were awful, one doctor said.

"There are a lot of feces everywhere: in the hallways, in the grass and all around," said Kim Kwiatek, a doctor with a FEMA medical assistance team from Ohio working at Biloxi Regional Medical Center.

At Biloxi Regional and Memorial Hospital at Gulfport doctors reported many cases of diarrhea, vomiting, skin rashes, and cuts from people moving debris. So far, doctors are not seeing the serious infectious diseases likely to breed when people are exposed to bad drinking water and fetid flood waters.

President Bush was scheduled to visit the Gulf Coast for the second time in four days today. Yesterday, he and first lady Laura Bush toured American Red Cross headquarters in Washington yesterday, thanking all for their work, asking the public for donations and showing confidence in the recovery effort.

Nonetheless, officials were put on the defensive again and again yesterday as reporters kept asking for some response to the criticisms.

CNN's Wolf Blitzer asked Chertoff: "Are you humiliated by what happened?"

Chertoff insisted that the scale of the calamity was so monstrous it overwhelmed any preparations that might have reasonably been made.

"It was unprecedented. ... Apocalyptic is the right description," Chertoff said. "We responded as rapidly as we could."

James Lee Witt, the Clinton administration FEMA director hired to advise Louisiana's governor, described the crisis yesterday in the state as "our worst nightmare."

Witt said yesterday that he thought the reorganization that put FEMA under the Department of Homeland Security had hurt the agency's ability to deal with natural disasters, and he said a lot of resources also had been depleted by the war in Iraq. But he declined to criticize federal, state or local officials in this disaster: "I think they worked as fast as they could to do whatever they could."

Rep. William J. Jefferson, a Democrat who represents the New Orleans area, was not so reticent. He criticized the government's push to get everyone out of the city in view of the danger of standing fetid water, downed power lines, no power and no clean running water.

Most of New Orleans' population of about 480,000 had by late yesterday either been moved to or were expected to be moved to shelters in 22 states as far north as Minnesota and west to California. Nearly half were in Texas alone.

This enormous population movement has touched off a kind of refugee crisis. Social service agencies, businesses, volunteer groups, military bases and other refugee shelters raced to help the multitudes find jobs, obtain their Social Security checks, receive their medicines, get their mail, locate missing relatives and pets, and enroll their youngsters in school.

Some had started looking for jobs, doing what they could to ease the nagging uncertainty.

Torres Smith, 42, a machine operator at a New Orleans seafood plant before Katrina hit, was evacuated along with his wife and four children, and is sleeping on a cot in the Astrodome.

"As far as I can tell, this is going to be our new home for a long time," he said. "I'll do anything -- cut grass, wash windows, wax floors. I can't just sit around here, looking at people lying in their cots."

The Associated Press and Sun staff writer Stephen Kiehl in Baton Rouge contributed to this article. Arthur Hirsch reported from Baltimore.

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