Updated

A stinging report issued by congressional investigators accuses the Department of Homeland Security of failing to prepare for and respond adequately to Hurricane Katrina, and blames the Bush administration for not having a clear chain of command to lead relief efforts.

The Government Accountability Office reported Wednesday that the administration still doesn't have a training program or catastrophic reponse plan ready to go in case of a storm similar to the Aug. 29 disaster in four Gulf Coast states.

It also charged that Homeland Security Department Secretary Michael Chertoff failed to serve as an overall storm coordinator and didn't assign anyone on the ground in the region to do so.

Leadership was "unclear," says the report, adding that the internal confusion, indecisiviness and failure to recognize the magnitude of the storm "serves to underscore the immaturity of and weaknesses relating to the current national response framework."

"No one was designated in advance to lead the overall federal response effort in anticipation of an event with clearly catastrophic potential consequences despite clear and repeated warnings by the National Hurricane Center," GAO Comptroller General David Walker told the House Government Reform Committee and Special Committee on Katrina. Walker added that a federal official should have been ready to step in as events became more dire.

But DHS spokesman Russ Knocke called the GAO's report "premature and unprofessional," and charged that the study is riddled with errors, particularly when it claimed the feds failed to call Katrina a catastrophic disaster.

"Apart from its obvious errors, it displays a significant misunderstanding of core aspects of the Katrina response that could have easily been corrected in the most basic conversations with DHS leaders," Knocke said in a statement.

He added that federal officials and supplies were already in the Gulf Coast before Katrina hit, and that the response plan for catastrophes is only used for unexpected disasters. The report did praise the Coast Guard, the Pentagon, the U.S. Postal Service and the National Finance Center for taking a "lean forward" approach to preparing for and responding to Katrina.

It also noted "a myriad of approaches and processes for requesting and providing assistance, and confusion about who should be advised of requests and what resources would be provided within specific time frames."

Meanwhile, at the Senate Homeland Security and Government Affairs Committee hearing, senators said they wanted to know why New Orleans city leaders apparently did not tell to Federal Emergency Management Agency officials early on that the New Orleans Convention Center had been opened as a shelter.

"I'm trying to get a clear picture of why the city sent people to the convention center when there was no supplies there, there were no supplies there, no security and why there wasn't communication with FEMA to ask for supplies?" asked Committee Chairwoman Susan Collins, R-Maine.

"We had people that were trapped and stranded on rooves on highways and at the convention center and [FEMA] didn't know about it? That's just impossible," responded New Orleans Mayor Ray Nagin.

Collins said she hopes Chertoff, and former FEMA Director Michael Brown, who was forced into early retirement as a result of his mishandling of the response, can explain how they didn't know about the convention center's shelter status.

Though Brown was named as the top federal officer in the Gulf Coast, his authority was unclear, the report found, leading to a "disjointed" response from all federal agencies.

The GAO report also takes Chertoff to task for declaring Katrina an "incident of national significance" on Aug. 30, one day after the storm hit, and why he didn't classify the storm as a catastrophic disaster.

"As a result, the federal response generally was to wait for the affected states to request assistance," the report found.

Asked by reporters whether Chertoff should have been the federal point person leading the response, Walker said President Bush has to make that decision.

"It could have been Secretary Chertoff, it could have been somebody on his staff," Walker said. "That's up to the president."

The House committee, chaired by Rep. Tom Davis, R-Va., is expected to release its findings by Feb. 15. Additionally, Collins' panel will conclude a separate investigation by mid-March, and the White House is completing its own review, conducted by homeland security adviser Frances Fragos Townsend.

"I'm very hopeful that our final report will answer a lot of questions the American people have," Davis said after being presented with the GAO report. "The most obvious being: How could our government fail so badly?"

Asked if New Orleans is ready for the next hurricane season, which begins June 1, Nagin said he hopes the levees and the core city will be rebuilt by then to withstand at least a Category 3 storm.

FOX News' Molly Henneberg and The Associated Press contributed to this report.