For Americans watching events unfold on television late last month, the arduous evacuation of New Orleans and the grandeur of the Olympic Games couldn’t have made for a starker contrast.

However one feels about its other policies, the Chinese government is clearly not afraid to invest in the future of its cities. The array of architecture it created for the Beijing Olympics was only part of a mosaic of roads, bridges, tunnels, canals, subway lines and other projects that have transformed a medieval city of wood and brick into a modern metropolis overnight.

Meanwhile, three full years after Hurricane Katrina devastated New Orleans, much of the city remains a wasteland. As Hurricane Gustav raced toward the Gulf Coast, it became clear that the city’s patchwork levee system could not guarantee the safety of its citizens. The evacuation of tens of thousands of residents was cheered as some sort of victory.

But for those with a sense of urban history, the tragedy of New Orleans is not just about governmental disregard for the welfare of the city’s inhabitants. It is about a lost opportunity. All of the great challenges that confront the 21st-century city — from class, race and environmental issues to the continuing duel between history and modernity — are crystallized in New Orleans.

Yet the kind of visionary urban plan that could address these issues in a bold and thoughtful way has yet to materialize. Instead, some of the country’s greatest architectural minds are inventing the future in cities like Beijing, Shenzhen and Dubai, where their talents are more appreciated.

The signs pointing to this tragic turn of events were there for anyone who cared to read them. The great urban planning experiments that transformed America in the early 20th century were both triumphs of engineering and dazzling monuments to a free, mobile society. Anyone who has watched the film “Chinatown” knows the story of William Mulholland’s aqueduct, which transformed Los Angeles from a desert wasteland into a sunny paradise of trim lawns and orange groves. Less known is the story of modern New Orleans, which exists because of the system of canals, levees and pumps — the largest in the world — that were used to drain acres of marshland.

This kind of bold government planning died long ago, of course, a victim of both the public’s disillusionment with the large-scale Modernist planning strategies of the postwar era and the antigovernment campaigns of the Reagan years. The consequences were obvious as soon as Katrina hit the Gulf Coast. And they have been reaffirmed many times since, with the collapse of the Interstate 35W bridge in Minneapolis and myriad accounts of our country’s crumbling infrastructure.

Still, many Americans stubbornly regard any kind of large-scale public works project with suspicion. Three years ago, for example, the nonprofit Urban Land Institute unveiled a master plan for New Orleans that would have transformed large parts of the city into wetland areas. But the proposal, which was released as thousands of people were struggling to make their way back to the city, caused a public outcry and was immediately dropped. The institute compounded the problem by not including a workable proposal for how to house those dislocated by the plan.

Since then, the most concrete proposal has been a plan by the official in charge of the city’s recovery, Edward J. Blakely, to identify 17 projects, from schools to community centers, that could be used to spur further development. But with a mere $400 million of public funds committed to the project, the plan is not likely to go far. (The city has hired the Boston firm Goody Clancy to prepare a citywide plan, but it is not scheduled for completion for another year.)

The lack of a coherent vision for the city’s future means that some of the most critical reconstruction decisions — like where to build — are left to private homeowners. The notion of concentrating the bulk of new construction on higher ground, an approach that would be both safer and environmentally sound, rarely comes up. Instead, FEMA’s distribution of relief money has sometimes encouraged people to rebuild in the most vulnerable low-lying areas, since it is used for repairing structures damaged by the storm, not for relocation. The perversity of such an approach can be seen in areas like Lakeview and the Ninth Ward, where the few scattered houses that have been rebuilt stand surrounded by acres of barren land, sometimes directly in the shadow of the levees.

When the government has been involved, it has often shown a callous indifference to the city’s architectural history. A few months ago, the Department of Housing and Urban Development began tearing down thousands of low-income housing units built in the late 1930s and early ’40s, including several low-rise brick apartment blocks in the working-class neighborhood of Tremé that were among the best early examples of public housing in the country. There have also been threats to demolish Charity Hospital, a towering Art Deco landmark near downtown, as well as several Modernist schools built in the 1950s and ’60s.

Not surprisingly, what little progress has been made has been the work of a few determined nonprofit organizations. In the Holy Cross neighborhood, Global Green built a prototype for a sustainable shotgun house, complete with solar panels, natural ventilation and recycled materials. The house is the first step toward creating a planned sustainable community, organized around a town green that is designed to collect runoff water during a storm.

Brad Pitt’s Make It Right foundation recently completed a competition for the design of several sustainable single-family houses, the first of which are now under construction in the Ninth Ward. And other organizations, like the local Preservation Resource Center, have been painstakingly restoring a number of historical houses throughout the city.

Yet these scattershot efforts, however noble, do not constitute a thoughtful, coordinated urban plan. Shoring up existing levees will not magically transform New Orleans into a model for the contemporary city.

To accomplish that, the city will have to start with a blueprint for preserving the historic fabric that was not destroyed by Hurricane Katrina — not just in tourist-friendly areas like the French Quarter, but across the city. It will need to tie efforts to rebuild the city’s infrastructure to a broader plan that takes into account its shrinking population, the realities of global warming and the racial and social patterns that have shaped New Orleans for decades. And that plan will have to integrate the needs of those who are still suffering the most: working-class people who don’t own their homes and can’t find an affordable place to live.

This will take real brainpower, of course. But the idea that it can’t be done — or that Americans can’t afford it — seems more ludicrous than ever, given the example of China. Sometime later this year, Steven Holl, one of the brightest talents working today, will complete his Linked Hybrid residential complex in Beijing. The project is both a model of sustainable design and a breathtaking example of how to build an urban community in the 21st century. The London-based engineering firm Arup is working on a master plan for an entire sustainable city, Dongtan, in a wetland area near Shanghai.

New Orleans, too, could become a bold vision — a laboratory for how to rebuild America’s faltering cities. It could evolve into a model for the future as compelling and optimistic as the one America offered to the world a generation ago. Or it could remain an emblem of how far we’ve fallen.

Nicolai Ouroussoff is the architecture critic for The New York Times, Previously, he had been the architecture critic for the Los Angeles Times. He was a nominated finalist for a Pulitzer Prize in 2004 for his work at the Los Angeles Times.