US politicians have joined calls from the public and the media for senior government officials to admit they were slow to respond to Hurricane Katrina.
President Bush has stood by his security and emergency teams
Two Senate panels are to hold inquiries as demands grow for the head of the Federal Emergency Management Agency (Fema), Michael Brown, to quit.
Homeland Security Secretary Michael Chertoff has also faced criticism.
President Bush, who will chair a probe into the disaster, backed both men and warned against playing a "blame game".
Widespread criticism of the Fema response reached a new high after an official memo showed that Mr Brown waited until hours after the storm made landfall before taking action.
Describing the storm as a "near catastrophic event", Mr Brown asked Mr Chertoff to authorise a 1,000-strong deployment of rescue and relief workers, but gave them 48 hours to reach the area.
He requested another 2,000 staff within seven days.
Last week, President Bush demonstrated support for Mr Brown on a visit to the Gulf Coast region, telling him: "Brownie, you're doing a heck of a job."
But critics in politics and the media have singled out Mr Brown for criticism, questioning his suitability for the job after a nine-year tenure as head of the International Arabian Horse Association.
Mr Bush briefed senior congressional leaders on Tuesday over plans to request new emergency funds to finance the ongoing rescue and relief effort in the states affected by the hurricane.
Away from the White House, though, even usually loyal Republican politicians have voiced their concerns over the way the crisis was handled.
The US government was criticised over the speed of its response
Mississippi's Republican Senator Trent Lott, who lost a home to the hurricane, singled Mr Brown out for criticism on US network CBS.
"If he doesn't solve a couple of problems that we've got right now, he ain't going to be able to hold the job, because what I'm going to do to him ain't going to be pretty," Mr Lott said.
Maine Senator Susan Collins, a Republican charged with leading an inquiry by the Senate Committee on Homeland Security, said she was concerned over how authorities would deal with a major terror attack.
"Governments at all levels failed," Ms Collins said.
"If our system did such a poor job when there was no enemy, how would the federal, state and local governments have coped with a terrorist attack that provided no advance warning and that was intent on causing as much death and destruction as possible?"
No blame yet
Mr Bush and Mr Chertoff have not escaped blame for the crisis in the Gulf states.
A CNN/USA Today Gallup poll published on Wednesday said that 42% of Americans rated the president's response as "bad" or "terrible".
Michael Brown (c) has borne the brunt of public and political criticism
Just 35% described his reaction as "good".
As homeland security chief, Mr Chertoff has faced some criticism over the department's primary focus on terror attacks and funding cuts imposed on Fema since it lost its independence and cabinet-level status.
Speaking on Tuesday, Mr Bush insisted that the time was not yet right to apportion blame.
"There will be ample time for people to figure out what went right, and what went wrong. What I'm interested [in] is helping save lives."