When the Levees Broke: A Requiem in Four Acts (premieres Mon.-Tue., Aug. 21-22, 9 p.m., HBO) "Thanks Katrina," reads a spray-painted message somewhere in the ruins of New Orleans, a mordant bit of gallows humor punctuated with a drawing of a heart split in two. When the Levees Broke, Spike Lee's four-hour "requiem" for the devastated city, is nothing if not a heartbreak. A mother recalls scanning the news for word of her 5-year-old daughter, whose corpse was identified by the backpack she always wore. A witness describes watching a husband try to lift his wheelchair-bound wife out a second-story window and onto their roof, his strength finally failing. A young man describes searching his mother's house for days before finding her buried under her refrigerator. Levees' first segment ends with footage of bodies left to bloat and decay in the rubble, testament to an overtaxed, unprepared and catastrophically mismanaged disaster response that failed on just about every level.

As anguished as it is outraged, Lee's capacious overview is a symphony of American voices, a great chorus of anger, sorrow and disbelief. Although Lee and his editors often pit opposing viewpoints against each other, the movie doesn't aim to synthesize a definitive portrait of Katrina and its aftermath. Lee airs without comment the allegation that levees protecting the city's Lower Ninth Ward were blown up to protect richer, whiter neighborhoods from flooding. True or not, the dispossession and abandonment that spawns such theories is real enough, and has a basis in history; during the floods of 1927, levees were indeed dynamited, flooding out more than a million residents. But, countering the idea that the response to the 1927 floods was colored by race, author John Barry points out that most of the disenfranchised were poor whites. "This was not about race," he says. "This was about money."

There is no lack of explanations for the ill-preparedness and incompetence of the national, state and local response to Katrina; blame runs from the city's former chief of police, who hysterically reported that babies were being raped in the Superdome, to mayor Ray Nagin and Louisiana governor Kathleen Babineux Blanco, who let the bad blood of an old political feud gnarl the lines of communication, through "heck of a job" Brownie and up to George W. Bush, who waited two weeks to put his feet on the ground, posing in front of a building that had been lit up to give the false impression that electricity had been restored.

But the pivotal question of the extent to which the torpid rescue effort was conditioned by the race, or class, of the hurricane's victims, is presented as a surprisingly open-ended one. Lee has never shied away from depicting American racism in crude, even cartoonish terms, but here he cedes the podium to other, often conflicting views. An NAACP lawyer's contention that the Gretna bridge incident, where Jefferson Parish police brandished shotguns to divert people they called "thugs," was unmistakably "a race thing," is followed by the testimony of two white residents who were similarly turned away. The tub-thumping tendencies that frequently derail Lee's fiction films are nowhere in evidence, despite the occasional off-the-wall assertion, of which Michael Eric Dyson's likening the removal of stranded evacuees to the kidnapping of slaves may be the most ludicrous.

Because Katrina's victims — or, to be more accurate, the victims of the country's failure to protect them — were, in Wolf Blitzer's memorable phrase, "so poor and so black," the extent to which their poverty or the color of their skin figured more prominently in the federal government's feckless response is impossible to gauge. As Levees' first act demonstrates, it was a toxic cocktail of racism and economic disempowerment that made New Orleans a disaster waiting to happen. Those who were shocked that the images of Katrina's aftermath looked like pictures from a Third World country were evidently unaware that New Orleans looked that way before Katrina as well — one reason why the flap over calling displaced Gulf Coast residents "refugees," rehashed here at some length, is itself offensive, as if comparing Americans driven from their homes to foreign victims of injustice were somehow an insult. Nearly a year after Katrina, the investigation into the government's massive failure to protect its citizens seems to have stalled, the buck stopped permanently with Michael Brown, the urgency of the nation's outrage dimmed by inflamed fears of foreign attack. Surely, we must think, such a thing could never happen again; we hope someone, somewhere, must be making needed improvements. But as another graffito, scrawled twice for added effect, reminds us, "Hope is not a plan."