New Orleans police are making the recovery of bodies of Hurricane Katrina victims top priority.
Police and soldiers are searching house-to-house as floods recede
Officials say initial estimates of some 10,000 dead in the southern US may prove exaggerated.
President George W Bush has urged national unity and invoked the response to the 9/11 attacks, a day before the fourth anniversary.
Vice President Dick Cheney is to visit evacuees in Texas, ahead of President Bush's third trip to the region.
The White House has removed US emergencies chief Michael Brown from his role managing the relief effort and recalled him to Washington.
In his weekly radio address, Mr Bush reminded the American public of the national unity after the attacks four years ago.
"Today, America is confronting another disaster that has caused destruction and loss of life. This time the devastation resulted not from the malice of evil men, but from the fury of water and wind," he said.
"America will overcome this ordeal, and we will be stronger for it.
"Four years later, Americans remember the fears and uncertainty and confusion of that terrible morning.
"But above all, we remember the resolve of our nation to defend our freedom, rebuild a wounded city, and care for our neighbours in need."
His comments have been criticised by opposition Democrats.
Senator Edward Kennedy said: "Four years after 9/11, as the administration's bungled response to Hurricane Katrina makes clear, we're obviously not adequately prepared to deal with another devastating attack."
Democrat senators have called for Mr Brown to be sacked for his response to the hurricane, which has caused devastating damage across southern states.
His role has been handed to Coastguard Vice-Admiral Thad W Allen, who has been overseeing relief and rescue efforts in New Orleans.
Homeland Security Secretary Michael Chertoff said he had directed Mr Brown to return to running the Federal Emergency Management Agency (Fema) nationally.
Mr Brown has been criticised over the slow pace of the rescue effort, amid allegations he does not have the experience to lead Fema.
New Orleans officials say the operation to save people stranded by the floods has now ended and efforts will instead turn to recovering bodies.
Police and soldiers will take on the grisly task of retrieving corpses, many of them tied to lampposts or left in houses marked with paint at the height of the floodwaters.
Col Terry Ebbert, homeland security chief for New Orleans, said early results suggested the death toll might not be as high as feared.
"Some of the catastrophic deaths that some people predicted may not have occurred," he said.
"Numbers so far are relatively minor as compared to the dire predictions of 10,000."
But the BBC's Daniela Relph says bodies can still be seen strewn in flood waters, along the roads and in houses.
A body lies in a New Orleans street more than a week after the storm
Recovery of remains will take priority over the forced removal of those New Orleans residents who still refuse orders to leave, officials added.
In the city itself, as the flood waters slowly recede, the streets are being swept, power lines repaired and supplies brought in.
Although renewed pumping from New Orleans has reduced water levels considerably, the army estimates it could still take weeks to complete the task.
Meanwhile, Mr Bush is to begin a third visit to the disaster zone on Sunday, with stops in both Mississippi and Louisiana, a spokesman said.
The BBC's Washington correspondent, Justin Webb, says that questions over Mr Brown's eligibility for his post have intensified political pressure on the White House.
Political figures in both the Republican and Democratic parties have accused the authorities of responding slowly.