WASHINGTON -- The largest sudden displacement of Americans since the Civil War has reverberated across the country from its starting point in New Orleans, as more than a half-million people uprooted by Hurricane Katrina have sought shelter, sustenance and the semblance of new lives.

Storm refugees overwhelmed the state of Louisiana and poured into cities from coast to coast, crowding sports arenas, convention centers, schools, churches and the homes of friends, relatives and even strangers.

Red Cross officials reported toward week's end that every shelter in a seven-state region was already full -- 76,000 people in Alabama, Mississippi, Florida, Georgia, Texas, Arkansas and Louisiana. Hundreds of miles from New Orleans, hotels were jammed or quickly filling.

Rich and poor alike, they found themselves starting over. The former began buying new houses and leasing new office space. The latter waited in lines for a bar of soap or a peanut butter sandwich.

Katrina has scattered more than twice as many people as the San Francisco earthquake of 1906, and unmoored more people in a few days than fled the Dust Bowl in the 1930s. Estimating from Census data, roughly 150,000 of the displaced lived below the poverty line even before they lost everything. Far more than 50,000 of them are past retirement age.

Cities and hamlets, charities and individuals stepped up to help. In Washington, District officials made plans to open a shelter in the D.C. Armory, and 415 retired veterans were moved from the Armed Forces Retirement Home in Gulfport, Miss. to a similar facility in the nation's capital.

"The biggest issue we're faced with is handling the volume of people," said Margaret O'Brien Molina, a spokesman for the Southwest region of the American Red Cross. "Just identifying their needs is so complex."

In Baton Rouge and other Louisiana cities, the influx was dangerously straining services, officials warned. Armed guards were stationed at food distribution sites, and Baton Rouge Police Chief Jeff LeDuff said the city's hospitals might have to be barricaded to prevent desperate storm victims from continuing to swamp emergency rooms. The city's sanitation system is overloaded, gasoline is scarce.

"Instead of water flooding in, we've got people flooding in," said Councilman Mike Walker of the East Baton Rouge Parish Council. "The levee of people broke."

Where to go? What to do? They needed food, water, medicine, beds, showers, toilets, clothing, jobs, schools, friends, diversions. Where to begin?

For many of the impoverished refugees from the Louisiana Superdome in New Orleans, the first step into the future led to a strip mall near the Astrodome, which transformed into a bazaar of free ham sandwiches, water, diapers, baby formula and other supplies brought by volunteers.

Gaynell Warden, 46, stood in her pajamas, 350 miles from home -- make that former home. For now and the knowable future, she lives in a new town of 25,000 comprised of cots in an old stadium. "My son is missing," she said. "I don't know if he's dead or alive."

Allen Porter, 18, sat in a hotel lobby in Hot Springs, Ark., 530 miles from his former home. His parents were out looking for a condominium while their son tried to sort out the confused picture that had seemed so clear and glittering just days before.

Senior year, top of his class at Jesuit High in New Orleans, Porter was a bit annoyed when his mother insisted on evacuating. He packed his iPod, "Wuthering Heights" and his applications to places like Princeton, Yale and Virginia. Now, his high school was reportedly under 13 feet of water, deep enough to drown his transcripts, and his khaki-clad buddies were scattered to the winds. "It could get lonely over time," he mused via the Internet.

Porter was probably wise to take the long view, because the few lessons available in upheaval of this scale suggest that the metropolis flung apart by the hurricane may still be in pieces years from now. More than 300,000 Japanese were left homeless by the Kobe earthquake in 1995, and some were still in makeshift camps three years later. Closer to home, the sudden influx of 125,000 Cubans in the 1980 Mariel boatlift was only partially absorbed by families and volunteers across the country; some of the refugees remained in camps into the late 1980s.

Herbert McKnight, 44, had no intention of waiting for New Orleans to be restored. "The way I'm looking at it, I don't have a job and I don't have a home," he said in Houston, where he and 20 members of his extended family were among the tens of thousands of displaced people occupying virtually all of the city's 55,000 hotel rooms. An accountant, McKnight said he was desperate to find work and to move into an apartment in Houston.

Mostly, though, it was a matter of coping with the here and now.

Internet bulletin boards buzzed with offers of spare bedrooms and pleas for volunteers. "I have 11 family members arriving," a harried host in Maryland began, and "a rental property in Capitol Heights, Md., to put them in. ... However, it is currently undergoing renovations and is not quite habitable yet. ... I need donations."

And: "I am in Kewanee, Ill., a small rural community in Illinois. ... I can fit 2-4 comfortably, ... 6-8 in a squashed condition."

School boards in state after state dropped their normal admission rules to make room for more than 100,000 school-age children from New Orleans and other storm-wrecked communities. Colleges and universities offered to reopen their rolls to take in some 50,000 displaced students.

But for some of the hardest-hit evacuees, such concerns seemed light years away. Those who were not moved to the Astrodome fanned out across Louisiana, swelling cities and towns to the bursting point and sorely testing the capacities of their neighbors.

In Baton Rouge, city officials said 20,000 refugees were being housed in official shelters, but they believe that's just the tip of the iceberg. Thousands more are thought to be staying in private homes, hotels and other facilities. And they are braced for more.

Rep. Richard Baker, R-La., said he planned to ask for temporary housing facilities from the Defense Department, the Department of Homeland Security and private companies and realtor groups. "Portable barracks, mobile homes, vacant commercial structures -- whatever can house people in humane conditions," he said.

More than 800 people were sleeping on blow-up beds on a gymnasium floor at Louisiana State University-Shreveport, where their living quarters aren't much larger than an average car. All of their belongings -- perhaps some clothes, toiletries and an old photo album -- are stacked by the beds. There's no other space for storage. Beds are crammed in like puzzle pieces, covering nearly every bit of the hardwood floor. Some residents plan to live in the gymnasium for at least the next month.

By mid-day Thursday, more than 1,000 refugees had found Starkville, a university town in northeastern Mississippi, according to Duane Tucker, disaster chairman for the local Red Cross chapter. "All the hotels in town are full, we've got people staying with relatives, and about 40 people from New Orleans living in a church shelter." And the problem is likely to worsen as middle-class families in hotels run out of money.

"I can't see the end," Tucker said.