NEW ORLEANS, Louisiana (AFP) -President George W. Bush was to tour parts of the southern United States still struggling in the wake of Hurricane Katrina as the nation marked four years since the September 11 attacks.

Much of New Orleans is still under water and rescue crews have been working around the clock to clear corpse-littered streets and get lingering residents to leave what has for 13 days been an almost entirely uninhabitable city.

Bush, who saw his popularity soar after the September 11 attacks, was keen to draw parallels between the two national disasters and to shake off the intense criticism that has dogged him over his handling of the hurricane relief effort.

Nearly two weeks after Katrina unleashed a humanitarian crisis of unprecedented proportions on the United States, the country was again &#34rebuilding a wounded city,&#34 he said in his weekly radio address.

But as police in New Orleans pushed on with the search for the dead, Bush came under renewed pressure, with separate polls giving him his lowest approval rating ever and criticising the botched federal response to the disaster.

An indication of the scale of the relief effort came with the American Red Cross appealing for 40,000 volunteers to help ease the misery of those left homeless, marking the biggest recruitment drive in its history.

&#34This is a disaster of such scope and such significance that it is not going to go away in weeks or even months,&#34 said John Degnan, spokesman for the organisation housing 160,000 refugees in 675 shelters across the country.

Bush was to arrive in the battered region later Sunday, his third visit since Katrina barrelled inland on August 29, destroying swathes of the jazz capital and displacing all but a handful of the city”s half-million population.

In his radio address, Bush vowed to make the region &#34more vibrant than ever&#34 but on the ground, life was still far from normal, with troops and police on the streets, little power and thousands of empty homes swamped by fetid water.

Troops in the city were carrying out door-to-door searches for survivors and holdouts, but the number of people needing rescue has dropped dramatically, officials said.

The city”s downtown district reverberated with the sound of jackhammers and heavy machinery, as work crews cleared out debris from the hurricane and looting to prepare for a months-long reconstruction drive.

&#34Today, America is confronting another disaster that has caused destruction and loss of life,&#34 Bush said, seeking to rally a nation showing little of the support it offered him in the wake of the September 11 attacks.

&#34This time the devastation resulted not from the malice of evil men, but from the fury of water and wind,&#34 he said.

&#34We are again being reminded that adversity brings out the best in the American spirit… Above all, we remember the resolve of our nation to defend our freedom, rebuild a wounded city, and care for our neighbors in need.

&#34America will overcome this ordeal, and we will be stronger for it.&#34

With polls by both Time and Newsweek magazines suggesting a majority of Americans are unhappy with his government”s response to the catastrophe, Bush highlighted the huge spending order in the Gulf Coast states.

The administration suffered its first political casualty of the hurricane on Friday when the head of Federal Emergency Management Agency director Michael Brown was pulled back to Washington and replaced by a coast guard vice admiral.

With the confirmed death toll approaching 400 across the region, a local disaster official said the number of bodies so far recovered from the receding floodwaters suggested that earlier estimates of 10,000 dead looked excessive.

Further optimism came from the army, which said that the putrid waters still covering entire neighbourhoods would likely be pumped out of New Orleans by next month — far sooner than expected.

&#34We have cut the time in half,&#34 said US Army Corps of Engineers spokesman Dan Hitchings in Louisiana state capital Baton Rouge. &#34We were looking at about 80 days and we have shortened it to about 40.&#34

Officials strove to paint ghostly New Orleans as a city emerging from the toxic sludge left by the hurricane, boasting a return to law and order and the reopening of its airport.

The commercial aviation director of the international airport, Roy Williams, said the hub would reopen to commercial flights Tuesday. The airport has handled only humanitarian and military flights since Katrina hit.

In New Orleans itself, paratroopers patrolled downtown, while marines searched the downtrodden Ninth Ward, near the French Quarter, where receding floodwaters left a thick residue of sewage.

Top military officials were urging residents still holed up in the watery city to leave but said no order to forcibly evacuate reluctant residents had yet been issued.

Police were also venturing into the foul waters of the city”s neighborhoods in a grisly search for bloated and decomposed bodies.

A detachment of sheriff”s deputies from Albuquerque, New Mexico launched 20 airboats onto the city”s flooded streets.

Asked whether his men had seen any bodies, Sheriff”s Deputy Nathan Lerner said: &#34They are everywhere. Can”t you smell them?&#34