Federal and local authorities today launched a concerted operation to recover the bodies of people who perished in New Orleans from the effects of Hurricane Katrina, and the nation's homeland security chief announced the replacement of Michael D. Brown as the top federal official on the scene of the Gulf Coast relief effort.

Officials in New Orleans wrapped up a search for survivors and began the body-recovery operation amid indications that the death toll may not be as high as previously feared.

In Washington, Homeland Security Secretary Michael Chertoff announced that he has recalled Brown, the embattled director of the Federal Emergency Management Agency, from his post as head of federal relief efforts on the ground in the Gulf Coast area and has replaced him with a senior Coast Guard officer.

He said Brown, who has come under heavy criticism for what is widely perceived as a slow and inadequate initial federal response to the disaster, will return to Washington and will remain as head of FEMA. Vice Adm. Thad W. Allen, the Coast Guard's chief of staff, will take over as the chief federal official in charge of Hurricane Katrina relief efforts, Chertoff said. He had named Allen to be Brown's deputy for the New Orleans area on Monday.

Brown said Chertoff told him of the change at 10 a.m. today.

Chertoff explained the recall of Brown and his replacement by Allen as dictated by a move to "the next phase of operations" in the hurricane relief effort. He said the FEMA director needs to be in Washington to carry out broader responsibilities, including potentially managing "other kinds of disasters" and dealing with additional hurricanes. He suggested that the change would also meet the need for a "seamless interaction with military forces" in the relief effort.

"Mike Brown has done everything he possibly could to coordinate the federal response to this unprecedented challenge," Chertoff said. The FEMA director "has got a lot of other responsibilities," he said, adding, "We cannot afford to let our guard down. I want to make sure FEMA continues to be run the way it needs to be."

Chertoff refused to answer questions about Brown's possible resignation or reports that the FEMA director embellished his resume.

He said that in New Orleans, a process is underway to recover the bodies of the dead "with dignity." Other officials have said that means reporters will be kept away from the scenes where corpses are located and retrieved. "I want to respect the privacy of the victims' families," Chertoff said.

In a news briefing outside the New Orleans city hall, Terry Ebbert, the city's homeland security director, said New Orleans police and soldiers from the National Guard and the Army's 82nd Airborne Division have combed all neighborhoods and "have evacuated all those people who wanted to leave their residences." Having concluded "the search for living individuals," Ebbert said, "what we're starting today . . . is a recovery operation" to search street by street for those who died.

He said death toll figures eventually will be released by state officials, but that initial indications are that the toll will fall far short of the 10,000 dead that Mayor Ray Nagin said had been projected by a computer model.

"I think that there's some encouragement in what we've found in the initial sweeps that some of the catastrophic death that some people predicted may not in fact have occurred," Ebbert said. "I think that we have great hope" based on the numbers of people rescued and evacuated "that the numbers so far are relatively minor compared to the dire projections of 10,000."

In a speech at the State Department, President Bush today expressed thanks for the world's "outpouring of compassion and support" for victims of Hurricane Katrina -- a display of sympathy he likened to that following the Sept. 11, 2001, terrorist attacks.

The NATO alliance in Brussels prepared to use military ships and planes to speed up delivery of European aid to the relief effort.

"In this time of struggle, the American people need to know we're not struggling alone," Bush said. "I want to thank the world community for its prayers and for the offers of assistance that have come from all around the world." Bush spoke at a swearing-in ceremony for longtime aide and confidante Karen P. Hughes, who is assuming the job of undersecretary of state for public diplomacy.

Bush's comments came as the White House made preparations for a third presidential trip to the devastated Gulf Coast this weekend. Bush planned to fly to Mississippi and Louisiana Sunday after marking the fourth anniversary of the Sept. 11 attacks, the White House said. He will make as yet unspecified stops to check on relief and recovery efforts, then return to Washington late Monday, the White House said.

In his speech, Bush stressed the enormity of the effort needed to recover from Katrina, which struck the Gulf Coast Aug. 29 with 140-mph winds and torrential rain. In addition to flattening structures on the Mississippi and Alabama coasts, the hurricane caused breaches in levees that protect low-lying New Orleans from adjacent Lake Pontchartrain, flooding some parts of the city up to rooftops.

"America is a strong and resilient nation," Bush said. "Our people have the spirit, the resources and the determination to overcome any challenge. And today this nation faces enormous challenges at home and abroad."

He praised a "substantial" outpouring of assistance, including contributions from some of the world's poorest countries.

Bush noted that Afghanistan has pledged $100,000 in aid, and Sri Lanka, an impoverished nation struggling to overcome the effects of last year's Asian tsunami, has sent a donation of $25,000. He also mentioned Canada's dispatch of ships laden with disaster supplies and planes to assist in the evacuation of survivors.

Israel and Italy have sent supplies such tents, mineral water, medical supplies, beds, blankets and inflatable rafts, Bush said. Kuwait has pledged $400 million in oil and $100 million in humanitarian aid, and Qatar and the United Arab Emirates have pledged $100 million each, Bush said.

"In all, more than 100 countries have stepped forward with offers of assistance, and additional pledges of support are coming in every day," he said, adding, "Four years ago, the American people saw a similar outpouring of sympathy and support when another tragedy struck our nation: the terrorist attacks of September 11th, 2001."

In New Orleans, soldiers and police went house to house to find residents still trying to hold out in the flood-damaged city and urge them to evacuate as ordered by the mayor. The soldiers and police were confiscating guns from residents and marking homes that contained bodies of hurricane victims.

But authorities said they were not forcibly removing people who refused to evacuate, despite the risk of disease from the filthy floodwaters -- filled with sewage, toxic pollutants and floating corpses -- that still inundate parts of the city.

Sherry Landry, the city attorney of New Orleans, told reporters, "At this time, force is not being used to evacuate" those who refuse to leave. However, checkpoints have been set up "to prevent the return of any person not specifically engaged in recovery efforts," she said.

"The city is now fully secured," Landry said, adding that 14,000 troops are now actively patrolling all areas of the city and running nightly air and ground reconnaissance missions to prevent further looting.

She said that if it becomes necessary for safety reasons, force will be used to evacuate people, but that "we're trying to make that a last resort."

P. Edwin Compass, superintendent of police in New Orleans, said officers have made more than 200 arrests as of this morning, mostly on weapons, looting and other state charges. He said police have not arrested any residents for refusing to evacuate.

Ebbert, the city's homeland security director, said local police and soldiers will identify locations containing bodies of hurricane victims and keep those places under observation until recovery teams organized by FEMA arrive to remove the corpses.

"To the best of our ability, we have thoroughly searched this city and have dealt with those individuals who want to be evacuated, and now we're back in a recovery operation for remains," Ebbert said.