President Bush mobilized a broad federal government response to the region devastated by Hurricane Katrina yesterday, ordering the Department of Homeland Security and a White House task force to coordinate an unprecedented recovery effort that he said could take years.

The response by numerous federal agencies will focus first on saving lives, rescuing people who have been trapped by floodwater and getting medical help to people injured in the storm. Federal officials said they will then turn largely to providing temporary shelter to hundreds of thousands of displaced people. Then they will focus on assessing the almost unfathomable infrastructure damage and draining New Orleans.

Michael Chertoff, secretary of homeland security, announced yesterday that the hurricane had been declared "an incident of national significance," invoking for the first time a plan that gives the relatively new federal department responsibility for coordinating the government's response to a terror attack or natural disaster.

"I anticipate this is going to be a very, very substantial effort," Chertoff said at a news conference where he said it was too early to estimate costs. "I don't even think we have fully assessed all of the collateral consequences that are going to have to be dealt with. We have a substantial challenge, but . . . we're going to do what it takes."

The Federal Emergency Management Agency has dispatched more than 50 medical assistance teams to the area along with 25 urban search and rescue teams with more than 1,000 personnel focused on saving lives and recovering bodies. FEMA is also working around the clock with the Army Corps of Engineers to try to fix the breached levees around New Orleans, which were allowing water to flow into the more than 80 percent flooded city.

Michael D. Brown, FEMA's director, asked Chertoff to make at least 2,000 DHS employees available for deployment to the region, according to a memo dated Monday. FEMA was looking for bilingual employees, and those with commercial driver's licenses and logistics skills.

Yesterday afternoon, Michael Leavitt, secretary of health and human services, declared a public health emergency for the entire Gulf Coast region, which speeds emergency health measures. Leavitt said the department plans to build 40 medical shelters with 10,000 beds and 4,000 medical personnel. The Centers for Disease Control and Prevention and the Food and Drug Administration assembled public health teams amid worries about chemicals and toxins, sanitation problems and mosquito-borne disease.

"We are gravely concerned about the potential for cholera, typhoid and dehydrating diseases that could come as a result of the stagnant water and the conditions," Leavitt said.

The Transportation Department's priority is evacuating residents, officials said, despite many impassable roads and bridges. Restoring minimal transportation infrastructure -- including highways, airports, seaports and oil pipelines -- has so far taken a back seat. Secretary Norman Y. Mineta said yesterday that 13.4 million liters of water, 10,000 tarps, 3.4 million pounds of ice and 144 generators have already been shipped to the region.

Though stretched by wars in Afghanistan and Iraq, the Defense Department said 11,000 National Guard members were at the disposal of governors to help with security and law enforcement, though no plans to send large numbers of active-duty troops are in place.

After Hurricane Andrew, a full brigade of the 82nd Airborne Division was dispatched to Florida to bolster security and to assist in humanitarian operations. Although federal law normally prohibits U.S. forces from engaging in law enforcement, some paratroopers were used to patrol streets.

Paul McHale, assistant secretary of defense for homeland security, said he expects a fleet of about 50 helicopters to support FEMA operations, and eight swift-water rescue teams have been sent from California. Eight naval ships are also slated to help with medical support, humanitarian relief and water transportation, and the hospital ship USNS Comfort is scheduled to arrive from Baltimore late next week.

Emergency experts said the two main issues facing the government are how to provide shelter for the displaced and how to recover from unthinkable economic losses. The experts said it is too early to measure the effectiveness of the emerging response, but they said it certainly will be a long road ahead.

"There are just so many problems to deal with right now, with looting, just trying to get in there and get the highways done, it's a huge, huge problem," said James Lee Witt, a FEMA director under President Bill Clinton. "I know they'll get a handle on it at some point, but it is going to be difficult."

Staff writer Bradley Graham contributed to this report.