WASHINGTON — Cartons of food, water, blankets, and other supplies to sustain 1 million people for three days were ready to be distributed today as FEMA anxiously eyed Louisiana levees to gauge how much damage Hurricane Gustav would wreak.

Flood barriers in and around New Orleans, which was devastated in 2005 by Hurricane Katrina, were expected to hold this time, the Federal Emergency Management Agency Deputy Director, Harvey E. Johnson, said. But the storm’s surge could overflow levees and at least partially flood the city, he said.

Damage from Gustav “will be a catastrophe by the time you add it all up,” Mr. Johnson predicted in an interview with The Associated Press before the hurricane hit landfall west of New Orleans, but not as bad as Katrina.

Gustav was downgraded to a Category 2 storm by midmorning today. Katrina was a Category 3 storm when it hit the Gulf Coast three years ago, obliterating 90,000 square miles and costing billions of dollars in damages. About 2 million people have been evacuated from Louisiana.

“We’re expecting levees to hold. We’re expecting that that people are much, much more prepared,” Mr. Johnson said. “We don’t expect the loss of life, certainly, that we saw in Katrina. But we are expecting a lot of homes to be damaged, a lot of infrastructure to be flooded, and damaged severely.”

The Homeland Security Secretary, Michael Chertoff, speaking from Baton Rouge, said he can’t remember a time when the Federal Emergency Management Agency was juggling so many major disasters at once.

“We do have the ability — to use the vernacular — to fight two wars at the same time,” Mr. Chertoff told The Associated Press in an interview.

In addition to Gustav, FEMA is also dealing with Hurricane Hanna, more than a dozen major wildfires across the country, flooding in eastern and northern Florida, and heavy precipitation predicted later this week over the panhandle and southern coast of Alaska.

“No doubt Hanna will present a different set of challenges,” Mr. Chertoff said. “At least one bright note — if there’s any bright note in having two hurricanes — is that it’s not coming on the same location.”

Forecasters predict Hanna could come ashore in Georgia and South Carolina late in the week. FEMA began preparing for Hanna several days ago and has designated a separate group of planners, Johnson said.

“We wanted to separate them so we’ll be as ready for Hannah as we are for Gustav,” Mr. Johnson said.

The government’s sluggish and bumbling response to Katrina shocked the world and turned FEMA into a national laughingstock. Follow-up investigations by Congress and the White House concluded that officials at the local, state and federal levels lacked a sense of urgency in preparing for catastrophic disasters.

The Army Corps of Engineers identified four Gulf Coast areas as particularly vulnerable to large storm surges according to internal administration briefing documents obtained by The Associated Press: Inner Harbor Navigational Canal at Seabrook, Gulf Intercoastal Waterway/Mississippi River Gulf Outlet, Saint Bernard, and Harvey Canal.

Mr. Johnson said FEMA has spent the last two years getting ready for the next big hurricane — which turned out to be Gustav. Response officials in Washington and along the Gulf Coast began gearing up last week, “almost as Gustav was born, and people saw the potential size of that storm,” Mr. Johnson said.

Over the past five days, he said, responders have been in a “H-minus-120 timeline,” double-checking to make sure all supplies, search-and-rescue teams, medical equipment, transportation systems, and shelters were ready to move 120 hours before the storm.

Aside from coordinating evacuation traffic, the government also spirited 3,000 residents from New Orleans by train and 5,000 by airplane, Mr. Johnson said.

“We all recall the visual images of the Coast Guard picking up people off rooftops in Katrina,” Mr. Johnson said. “I don’t think we’ll see as much of that this year because so many people evacuated very wisely.”