Imagine building a city from scratch. Now, imagine doing it in just a few months — dozens of times over.

That's the challenge facing federal officials as they scramble to house up to 300,000 people in Louisiana, Mississippi and Alabama displaced by Hurricane Katrina (search).

The solution is mind-boggling in its scope and complexity: Build dozens of temporary cities of up to 25,000 homes from the ground up. The ambitious resettlement plan is unprecedented in U.S. history, experts say, and raises huge logistical questions that, in most cases, have yet to be answered — or even anticipated.

"The whole process is just staggering," said Rolf Pendall, professor of urban and regional planning at Cornell University (search). "I'm left speechless by the prospect of getting people resettled and giving them a semblance of their former life."

Marion Orsini, 75, moved into an air-conditioned trailer last week at the end of a dirt road in remote Patterson. Orsini, who has no family and is disabled from a stroke six years ago, doesn't know what happened to his former neighbors, his car is flooded and he doesn't know when — or if — he can go home.

He feels isolated in the trailer, which is located 90 miles southwest of his former New Orleans home. He has no way to get to the store and relies on another evacuee for food and supplies.

"I'm at the end of my life and I never knew I'd be relying on someone like this," said Orsini, holding back tears. "When I wanted something, I'd go out and get it."

Officials with the Federal Emergency Management Agency (search) and the Department of Housing and Urban Development (search) have yet to answer many questions involved in the plan.

The settlements would range from 2,000 to 25,000 units — mostly prefabricated houses and mobile homes — arranged in loose street grids. They will ideally be placed within a short drive of pre-existing shopping centers, grocery stores and gas stations to make life easier for evacuees.

It's still unclear, though, where exactly the cities will be established and how the neighboring communities will cope with the thousands of extra people using their roads, schools and police forces overnight.

At least three major government contractors — one for each state — were scouting locations and negotiating with local officials. In Mississippi, several dozen engineers from Bechtel Corp (search). were at work this week and thousands of travel trailers were expected in the coming weeks, said Brenda Thompson, company spokeswoman.

Fluor Corp. (search) has a $100 million contract to handle housing in Louisiana, while CH2M Hill (search) is coordinating efforts in Alabama.

Federal officials stress that nothing will be done without the consent and support of local agencies. But experts in urban planning say tensions are inevitable — particularly racial and socio-economic tensions as evacuees from poor, urban areas move into outlying, more affluent communities.

Pendall, the Cornell professor, said existing infrastructures could be strained.

"You need to think about not only the cost of building what's on site for those people, but also for all the infrastructure for those people who will be nearby," he said. "That's a very tall order and it's probably a recipe for a lot of resentment and backlash pretty fast if the communities have infrastructure systems that break down."

Some residents of Baton Rouge have complained to police about problems from the influx of evacuees that has nearly doubled that city's population.

Experts say that paying attention to the evacuees' emotional and social needs when the cities are laid out can go a long way toward easing such issues. Giving people a sense of control over their new lives can help do that, they said.

In Kobe, Japan, where 150,000 people were placed in temporary housing after the 1995 earthquake, officials found that the most crucial factor for evacuees' mental health and economic success was being close to their old homes and jobs, said Bob Olshansky, a professor of urban and regional planning at the University of Illinois, Urbana-Champagne (search).

Other important factors were keeping old neighbors together and routinely surveying the displaced residents so that adjustments could be made in funding to meet their evolving needs, Olshansky said. Planners also learned from their mistakes: They initially worried too much about how much housing they needed without paying enough attention to the housing type or location.

The transition proved hard in Kobe. The 48,000 units were built to last two years, but 5,000 homes were still occupied four years later, Olshansky said. Some people never moved back to their old homes and remain in the units, which have now been converted to public housing.

That's something that New Orleans native Betty Romero can't understand.

"We've had a setback, but we'll come back," said Romero, 56, who's sharing a cramped FEMA trailer with her daughter, son-in-law, granddaughter and pet Chihuahua. "I don't care if I have to sleep in a trailer or in a car, I'm not leaving New Orleans. I have roots."