WASHINGTON — For the next few days, federal help to Katrina-ravaged areas of the Gulf Coast will be a matter of life and death. It's a "golden 72 hours" with the clock ticking for dramatic rescues of people stuck in high water or trapped in rubble.

The federal job then will become much tougher — rebuilding ravaged areas in Louisiana, Mississippi, Alabama and beyond.

The reconstruction after Katrina likely will be the biggest recovery program in U.S. history, dwarfing 1992's Hurricane Andrew and 2001's terror attacks, veteran emergency managers said.

Andrew, the costliest hurricane and natural disaster on record, caused what would be the equivalent of $43.7 billion in damages in 2004 dollars. Experts said it's premature to put a cost on Katrina's damage.

Too much water and too few places to live will be urgent problems facing the first rescuers. "It's going to be bad," said Eric Tolbert, former chief of disaster response for the Federal Emergency Management Agency (FEMA). "I have to believe this one [recovery operation] will be larger than Andrew. We're talking about a very intense three- to five-year recovery operation."

By late yesterday, New Orleans and much of the Gulf Coast still were too flooded to make an assessment. It was too dangerous for federal and state officials to fly an airplane to get even a cursory idea of the damage, Louisiana Gov. Kathleen Blanco said in a news conference in Baton Rouge.

"I'm begging for patience," Blanco said.

President Bush, at an RV resort and country club in Arizona, said: "I want the folks there on the Gulf Coast to know that the federal government is prepared to help you when the storm passes."

The federal government is mobilizing thousands of truckloads of recovery supplies: ice, water, food, temporary shelters and generators. Thirty-eight search-and-rescue and medical teams were waiting for the storm to subside so they could enter the damage areas, according to FEMA.

The American Red Cross said it launched its "largest mobilization effort in history" for Katrina.

Beyond hampering search-and-rescue and recovery procedures, the flooding could produce illnesses.

Because some of that high-standing water could be mixed with sewage from damaged wastewater plants, there's a good chance of spreading disease, former Florida emergency-management chief Joe Myers said.

"What's critical right now is the depth of water," said Tolbert, now a Charlotte, N.C., disaster consultant. "Re-entry [to some areas] may not even begin for weeks or months."

That will make housing a big problem.

After last year's quadruple hurricane strike, FEMA has about 18,000 trailers that could be used as temporary homes, but as many as 40,000 probably will be needed because of the size, location and scope of Katrina's strike, Tolbert said.

"You've got displaced people. What about all those people in the Superdome?" Myers asked. "It's like going to a ballgame for a month, because where are you going to go? Their homes are underwater."

Disasters of this scope in the United States play out in all-too-familiar ways.

The next couple of days are crucial, called the "golden 72 hours" in emergency-management parlance, much like the golden hour for heart-attack patients, said Tolbert, North Carolina's former disaster chief.

Life hangs in the balance for three days. No one argues. Everyone just acts. There will be incredible and inspiring stories of survival amid the rubble.

Frustrations then will probably set in.

"The first trigger after a disaster is three days afterward," Myers said. "It's how visible the government is in their getting ice and water [to victims]. By Thursday evening, Friday morning, going into the weekend, there better be a lot of ice and water and fans."

The Bush administration doesn't want to follow in the footsteps of the first Bush presidency when Miami's disaster chief asked three days after Andrew hit: "Where the hell is the cavalry?"

The biggest government spending and hardest work will come when the public's attention wanes and the real rebuilding begins.

That's when increased inspections find big problems in infrastructure such as sewer plants, roads, bridges and historic buildings. It's when government officials have to make hard decisions on what to rebuild, when and how.

"During the immediate postcrisis phase, everybody's focused on saving lives. Everybody's in agreement on what to do," said Michael Lindell, director of the Hazard Reduction and Recovery Center at Texas A&M University. "The agreement starts to unravel in the short term and into the recovery. People have different agendas."

And the recovery will be patchy.

"Some areas are going to be back to normal in weeks to months," Lindell predicted. "But there are pockets that may take a very long time and might not ever really recover."