Days after Katrina moved on, victims and rescuers remained focused on a race for recovery in which every hour, every minute was crucial. But long after food and water supplies are restored to a desperate city, after the looting is checked and the last body buried, New Orleans' road back from devastation will be measured in years.

There are voices of nihilism about the city's prospects. House Speaker Dennis Hastert stirred up a storm of criticism when he said it doesn't make sense to rebuild the battered metropolis -- a remark from which he has since climbed down. But most experts and politicians seemed to agree that the city founded nearly three centuries ago will be reborn.

In ways that are difficult to predict, however, New Orleans is likely to be a significantly altered city from the one that existed before it was invaded by the waters of Lake Pontchartrain.

"It will be a different place physically; it will be different socially; it will have a different sense of place,'' said Susan Cutter, a professor of geography at University of South Carolina and director of the school's Hazards Research Lab.

Along the way, residents, planners and officials will face profound engineering, financial and social challenges.

Experts note that a long line of other cities have rebuilt from similarly devastating natural and man-made assaults -- Galveston from the great hurricane of 1900, San Francisco from the earthquake of 1906, the cities of Europe and Japan from the bombs of World War II.

"Galveston and San Francisco weren't heavily populated, relatively speaking, and they weren't necessarily complex urban areas," said Cutter, who also is a consultant to the Department of Homeland Security. "World War II bombing may be a closer example, but those populations were displaced for decades."

Mary Comerio, a professor of architecture at the University of California at Berkeley who has written extensively on recovery from earthquakes, said, "It's not so different from what happened in Kobe, Japan, [in the earthquake of 1995]. It was an equally horrific experience. Four hundred thousand housing units were uninhabitable; half of them were destroyed. It cost about $90 billion to repair."

Others point out that there is nothing certain about the recovery process.

Joel Kotkin, the author of "The City: A Global History," noted that Galveston, while rebuilt and strengthened against future storms, never regained the leading economic position that it held before the hurricane of 1900.

"Houston took over almost entirely" as the port headquarters of Texas, he said.

The first tasks

Beyond restoring order, the first and most obvious challenges for New Orleans are to get the water pumped out and basic services turned on.

"I think we're talking about months to get the lights and water on," said Comerio, author of the book, "Disaster Hits Home." "It will take 10 or 15 years to see some kind of finished city."

After the existing levee breaches are restored will come more complex issues of how to rehabilitate and presumably improve the city's defenses against nature for the longer term. Those will involve not just questions of engineering but of city design and social equity.

Can something approximating the footprint of the pre-Katrina New Orleans be restored and protected or should the city cede to nature some neighborhoods, many of them poorer neighborhoods, that proved particularly vulnerable last week?

Those lucky enough to get out were part of a vast exodus that has spread New Orleans residents across the South and beyond. Plans for the city's future rest in part on how many of them will return and how many will seek lives elsewhere.

Compounding the city's difficulties are the psychic as well as physical damage from the perception of a tardy and incompetent response to the tragedy by public officials.

"New Orleans' [government] is famously inefficient and corrupt, so that adds to the challenge," said Kotkin.

In an essay in last week's edition of City Journal, Nicole Gelinas wrote, "[New Orleans'] decline over the last three decades has left it impoverished and lacking the resources to rebuild its economy from within. New Orleans can't take care of itself even when it's not 80 percent under water; what is it going to do now, as waters continue to cripple it and thousands of looters systematically destroy what Katrina left unscathed?''

Comerio said that images of government inadequacy and violence perpetrated by former neighbors made New Orleans unique among the recent disasters she has studied.

"There's a huge sense of distrust on the part of the population that's there," she said, "There's a very difficult healing process that's going to have to go on."

While people are starving and dying, considerations about whether New Orleans can recapture its charm and atmosphere are necessarily pushed aside. But in the longer term, they will be important to a city trying to regain a sense of its pre-deluge self.

New Orleans' civic character has always been seen as unique; part of the popular tourist city's appeal came from it sometimes seedy authenticity. In restoring flood-damaged neighborhoods, said Cutter, "There is a danger that you will restore it into a kind of theme park New Orleans."

Kotkin said, "One of the things people liked about it was the kind of funky little lunch places, the less-predictable kind of places. I think a lot of that will be lost. I think a real concern is that you'll get a new faux New Orleans that will be more Anaheim than antebellum."'

Of course, no one yet has a handle on how much it will cost to rebuild the city.

"You saw early estimates of insurance losses of $16 to 25 billion, which have to be way low," said David Dzombak, a professor in the department of civil and environmental engineering at Carnegie Mellon University. "I couldn't guess the entire cost, but I expect it to be several-fold that, at the least."

Plenty of warning

The decades-long struggle to protect New Orleans against the water that was its reason for being began on a federal level after the great Mississippi River flood of 1927, an inundation that killed more than 1,000 across the South.

The damage persuaded Congress to authorize the U.S. Army Corps of Engineers to strengthen levees along the Mississippi and re-engineer the river's channel.

That effort has been largely successful. The waters on the river side of New Orleans remained within their banks throughout the devastation of last week, as they have for decades.

On Sept. 9, 1965, however, the threat to the city from the other side, from the banks of Lake Pontchartrain, was dramatically demonstrated as Hurricane Betsy roared ashore and sent the lake waters over the crest of existing levees. That prompted the release of more federal dollars allowing the Corps to strengthen the levees on the lake shore to the city's north.

But Betsy was only a Category 3 hurricane. It occurred during years now viewed as a relative lull in hurricane activity in the Atlantic Ocean and Gulf of Mexico, and those factors informed the design of the bolstered defenses that were built along Lake Pontchartrain.

Decades later, as supercomputers became available for meteorological modeling, experts began to reassess the potential threat of a stronger storm. The results were startlingly accurate predictions of just the kind of devastation that occurred last week.

New Orleans and the nation were repeatedly warned of the deadly consequences of a Category 4 or 5 hurricane in an acclaimed five-part series in the New Orleans Times-Picayune in 2002 and in subsequent articles in other publications, including The New York Times, National Geographic and Civil Engineering Magazine.

With the prescience of those warnings so starkly demonstrated, officials soon will return to the debate over how to protect the region from the next "Big One."

"Just getting the water out is a very big challenge in and of itself," said Carnegie Mellon's Dzombak. "You see estimates of 30 days, but some of the things you read in the literature suggest that it could take considerably longer than that."

After that, he said, New Orleans faces "some very hard decisions about where and how to rebuild and whether certain parts of the city should even be rebuilt."

To rebuild or not

One option is to construct a more effective version of the same levee system that failed last week. There are alternative proposals to wall off portions of the city, Dzombak noted, "something like bulkheads in a ship so you could have an opportunity to isolate the damage."

Dzombak said experts may consider but probably will quickly answer "yes" to the threshold question of whether to rebuild the city in its current location at all.

"I don't think there will be any real thought to abandoning the city, but certainly parts of it will be tougher to justify [rebuilding] than others," he said.

"From a political and moral sense, I don't see that you have much choice," said Brian Wolshon, a professor of civil engineering at Louisiana State University. "What else do you do with it? You have an enormous amount of built infrastructure and value there."

A 2003 study in Civil Engineering Magazine noted that Joseph Suhayda, an LSU oceonographer who was one of the first scientists to model and forecast the effects of a Katrina-strength storm on New Orleans, proposed a kind of civic redoubt in the core of the city.

He envisioned a levee system surrounding the central business district that would contain significant historical areas, including the French Quarter, so that the city would be able to protect not only those neighborhoods but provide a vastly larger area of shelter in a catastrophic storm.

His proposal, offered in the mid-1990s, was criticized at the time by, among others, the Corps of Engineers, which was just beginning to study the creations of a more extensive system of defenses against a category four or greater storm.

A still more ambitious proposal to protect the city in the long run involves redirecting the path of the Mississippi River.

In addition to Pontchartrain on its north, New Orleans is bordered on the east by Lake Borgne. According to Civil Engineering Magazine, Roy Dokka, a geologist at LSU, has predicted that the constant pattern of subsidence in southern Louisiana means that Pontchartrain and Borgne will merge into a single body of water opening onto the Gulf within a century.

By redirecting the mighty river into the merged lake, he has argued, engineers could harness the sediment that flows through it to bolster the city's north shore, which then would border one of the world's largest harbors.

Planners must, in any case, deal foremost with how such decisions would affect people. Extensive flooding of the upper Midwest in the 1990s, along with the costs of Hurricane Andrew, which devastated parts of Florida in the same decade, spurred changes in federal rules to make it more difficult to rebuild in areas prone to floods and other storm damage.

Those considerations will significantly influence the civic triage New Orleans is about to go through in deciding where and how to rebuild itself.

"Perhaps you don't encourage the residential development in some of the lower lying areas, Dzombak said, "Those are some of the tough decisions ahead."

Who will return?

While thousands of New Orleans residents continue to wait for rescue or relief, most residents of the city who evacuated before Katrina now are widely scattered. How long their exile will last is another question mark over the city's future.

The superintendent of Louisiana schools advised parents on Thursday that they should try to enroll their children in schools wherever they find themselves, rather than wait for New Orleans classes to reopen. At least some of those transplants likely will become invested in their new communities and never go back to New Orleans.

"A lot of people are not going to return," said Cutter. "One of the things people seek to regain from a mental health perspective is to try to regain some sense of normalcy; you've got to get the kinds in school, you've got to get back to your routine things."

How this self-selection of permanent emigration will vary across different demographic groups is another open question.

"People who own property and have insurance will go back," said Comerio. "One of the hardest challenges will be providing some degree of assistance and security for the poor who don't have insurance, who may not have jobs. How they will restart their lives is a very big issue."

Kotkin said, "The danger is that the people with anything going for them will start new lives in other places.

If you're a nurse, a teacher, a machinist, you could very well find a job elsewhere in some place with a better economic climate. What you may have returning are people who are less productive and more dependent on government."

LSU's Wolshon notes that the litany of future concerns goes on. "I'm not an expert on this but you have to wonder aloud what Fortune 500 company is going to want to put their regional headquarters in a city which has been uninhabitable for two months?"

But for all those daunting challenges, Wolshon, who consulted on the city's evacuations plan, predicted that most of those who fled will return home.

"This, too, shall pass; the vast majority of people are going to come back," he said. "This is their roots. This is where their lives are.''