WASHINGTON THE white people got out. Most of them, anyway. If television and newspaper images can be deemed a statistical sample, it was mostly black people who were left behind. Poor black people, growing more hungry, sick and frightened by the hour as faraway officials counseled patience and warned that rescues take time.

What a shocked world saw exposed in New Orleans last week wasn't just a broken levee. It was a cleavage of race and class, at once familiar and startlingly new, laid bare in a setting where they suddenly amounted to matters of life and death. Hydrology joined sociology throughout the story line, from the settling of the flood-prone city, where well-to-do white people lived on the high ground, to its frantic abandonment.

The pictures of the suffering vied with reports of marauding, of gunshots fired at rescue vehicles and armed bands taking over the streets. The city of quaint eccentricity - of King Cakes, Mardi Gras beads and nice neighbors named Tookie - had taken a Conradian turn.

In the middle of the delayed rescue, the New Orleans mayor, C.Ray Nagin, a local boy made good from a poor, black ward, burst into tears of frustration as he denounced slow moving federal officials and called for martial law.

Even people who had spent a lifetime studying race and class found themselves slack-jawed.

"This is a pretty graphic illustration of who gets left behind in this society - in a literal way," said Christopher Jencks, a sociologist glued to the televised images from his office at Harvard. Surprised to have found himself surprised, Mr. Jencks took to thinking out loud. "Maybe it's just an in-the-face version of something I already knew," he said. "All the people who don't get out, or don't have the resources, or don't believe the warning are African-American."

"It's not that it's at odds with the way I see American society," Mr. Jencks said. "But it's at odds with the way I want to see American society."

Last week it was how others saw American society, too, in images beamed across the globe. Were it not for the distinctive outlines of the Superdome, the pictures of hovering rescue helicopters might have carried a Somalian dateline. The Sri Lankan ambassador offered to help raise foreign aid.

Anyone who knew New Orleans knew that danger lurked behind the festive front. Let the good times roll, the tourists on Bourbon Street were told. Yet in every season, someone who rolled a few blocks in the wrong direction wound up in the city morgue.

Unusually poor ( 27.4 percent below the poverty line in 2000), disproportionately black (over two-thirds), the Big Easy is also disproportionately murderous - with a rate that was for years among the country's highest.

Once one of the most mixed societies, in recent decades, the city has become unusually segregated, and the white middle class is all but gone, moved north across Lake Pontchartrain or west to Jefferson Parish - home of David Duke, the one-time Klansman who ran for governor in 1991 and won more than half of the state's white vote.

Shortly after I arrived in town two decades ago as a fledgling reporter, I was dispatched to cover a cheerleading tryout, and I asked a grinning, half-drunk accountant where he was from, city or suburb. "White people don't live in New Orleans," he answered with a where-have-you-been disdain.

For those who loved it, its glories as well as its flaws, last week brought only heartbreak. So much of New Orleans, from its music and its food to its architecture, had shown a rainbow society at its best, even as everyone knew it was more complicated than that.

"New Orleans, first of all, is both in reality and in rhetoric an extraordinarily successful multicultural society," said Philip Carter, a developer and retired journalist whose roots in the city extend back more at least four generations. "But is also a multicultural society riven by race and class, and all this has been exposed by these stormy days. The people of our community are pitted against each other across the barricades of race and class that six months from now may be last remaining levees in New Orleans."

No one was immune, of course. With 80 percent of the city under water, tragedy swallowed the privilege and poor, and traveled spread across racial lines.

But the divides in the city were evident in things as simple as access to a car. The 35 percent of black households that didn't have one, compared with just 15 percent among whites.

"The evacuation plan was really based on people driving out," said Craig E. Colten, a geologist at Louisiana State University and an expert on the city's vulnerable topography. "They didn't have buses. They didn't have trains."

As if to punctuate the divide, the water especially devastated the Ninth Ward, among city's poorest and lowest lying.

"Out West, there is a saying that water flows to money," Mr. Colten said. "But in New Orleans, water flows away from money. Those with resources who control where the drainage goes have always chosen to live on the high ground. So the people in the low areas were hardest hit."

Outrage grew as the week wore on, among black politicians who saw the tragedy as a reflection of a broader neglect of American cities, and in the blogosphere.

"The real reason no one is helping is because of the color of these people!" wrote "myfan88" on the Flickr blog. "This is Hotel Rwanda all over again."

"Is this what the pioneers of the civil rights movement fought to achieve, a society where many black people are as trapped and isolated by their poverty as they were by legal segregation laws?" wrote Mark Naison, director of the urban studies program at Fordham, on another blog.

One question that could not be answered last week was whether, put to a similar test, other cities would fracture along the same lines.

AT one level, everything about New Orleans appears sui generis, not least its location below sea level. Many New Orleanians don't just accept the jokes about living in a Banana Republic. They spread them. But in a quieter catastrophe, the 1995 heat wave that killed hundreds of Chicagoans, blacks in comparable age groups as whites died at higher rates - in part because they tended to live in greater social isolation, in depopulated parts of town. As in New Orleans, space intertwined with race.

And the violence? Similarly shocking scenes had erupted in Los Angeles in 1992, after the acquittal of white police officers charged with beating a black man, Rodney King. Newark, Detroit, Washington -all burned in the race riots of the 1960's. It was for residents of any major city, watching the mayhem, to feel certain their community would be immune.

With months still to go just to pump out the water that covers the city, no one can be sure how the social fault lines will rearrange. But with white flight a defining element of New Orleans in the recent past, there was already the fear in the air this week that the breached levee would leave a separated society further apart.

``Maybe we can build the levees back," said Mr. Carter. ``But that sense of extreme division by class and race is going to long survive the physical reconstruction of New Orleans."

Copyright 2005 The New York Times Company. Reprinted from The New York, Week in Review, of Sunday, September 4, 2005.

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