Republican leaders sought to take the lead on a congressional investigation of the federal government's response to Hurricane Katrina (search) on Wednesday as criticism of the Bush administration continued to build.

"Americans deserve answers. We must do all we can to learn from this tragedy, improve the system and protect all of our citizens," House Speaker Dennis Hastert (search) and Majority Leader Bill Frist (search) said in a statement.

They said a bipartisan committee of senior lawmakers would be formed to review the preparation for and recovery efforts after Katrina, which has killed an untold number of Americans and left thousands homeless and jobless. The committee's report would be due on Feb. 15 next year.

After praising first responders for their work on the ground and Congress for passing a $10.5 billion aid package last week, Hastert and Frist said, "But we all agree that in many areas, the initial relief response to Hurricane Katrina was unacceptable at the local, state and federal level."

Congressional Democrats were notified of the Republicans' plan but not consulted. Senate Minority Leader Harry Reid responded by calling for an independent commission.

"Democrats strongly prefer that the federal government's unacceptable response to Hurricane Katrina be investigated by a commission of independent experts like the 9/11 commission. An independent investigation would be insulated from politics and avoid the conflicts of interest inherent in an investigation of a Republican administration by a Republican-controlled Congress," a Reid spokesman said.

Top Democrats came out in force on Wednesday to slam the administration's handling of the Katrina emergency, even as Bush announced he would seek another $51.8 billion to cover the costs of federal recovery efforts. Congressional officials said they expected to approve the next installment as early as Thursday, to keep the money flowing without interruption.

But with the anniversary of the Sept. 11, 2001 (search), attacks looming, Democrats and even some Republicans were furious that the nation was not more prepared for Katrina.

Sen. Hillary Rodham Clinton sought an independent commission to study the response and made the rounds of four network morning television shows, taking on Michael Brown, director of the Federal Emergency Management Agency (search).

"I would never have appointed such a person. I would imagine, I don't think that anybody would. You would appoint somebody who has experience," Clinton told CBS.

Clinton, along with Maryland Sen. Barbara Mikulski, introduced a bill that would restore FEMA's independence and Cabinet-level status. The Bush administration had tucked the agency under the umbrella of the Homeland Security Department.

Meanwhile, Rep. Nancy Pelosi, D-Calif., renewed her call for Brown's dismissal. "There were two disasters last week: first, the natural disaster, and second, the man-made disaster, the disaster made by mistakes made by FEMA," she said.

She told reporters she had urged Bush in person at the White House on Tuesday to fire Brown.

"Why would I do that?" Pelosi quoted the president as saying.

"'I said because of all that went wrong, of all that didn't go right last week.' And he said 'What didn't go right?"'

"Oblivious, in denial, dangerous," she added.

While many Democrats have restrained themselves from openly criticizing the president on the war in Iraq or missteps surrounding the Sept. 11 attacks, the Katrina disaster has given them occasion to abandon such caution.

"It is different when you face a foreign enemy on the one hand versus a domestic failure on the other," Democratic consultant Mark Mellman said.

"Democrats see a real problem with the way this administration has handled Katrina, and see real needs that have to be addressed. Everybody is trying to do the best they can to help these victims," Mellman said.

Republicans have accused Democrats of seeking political advantage in attacking the administration's response.

"While countless Americans are pulling together to lend a helping hand, Nancy Pelosi and Harry Reid are pointing fingers in a shameless effort to tear us apart," Republican Party chief Ken Mehlman said Wednesday in a statement.

Bush's spokesman, Scott McClellan, said the White House is "focused on bringing everybody together to help the people in the region. And the president continues to act to make sure that we're addressing the ongoing problems," he said.

McClellan took issue with what he called "personal attacks" by Democrats, particularly Reid's implication that Bush's Texas vacation may have hindered the federal response to Katrina.

Adding to the rising partisan temperatures, the liberal advocacy group MoveOn.org announced a protest demonstration in front of the White House on Thursday afternoon by storm evacuees. And Democratic Party Chairman Howard Dean, speaking at a Baptist convention in Miami, said, "Americans deserve better from their leaders."

Bush cut short his vacation by two days last week to return to Washington. He has presided over daily meetings, visited stricken Gulf Coast areas twice and was expected to return soon. He has sent Cabinet members to the region; Vice President Dick Cheney planned to be there on Thursday.

On Wednesday, the White House announced Bush is asking lawmakers to approve another $51.8 billion to cover the costs of federal recovery efforts. That is in addition to $10.5 billion already approved.

Included in the request are $1.4 billion for the military and $400 million for the Army Corps of Engineers (search), which is working to plug breached levees that submerged most of New Orleans and to drain the city of the rank floodwaters, McClellan said. The rest would go to FEMA.

Also on Wednesday, the government announced it would to distribute debit cards worth $2,000 to victims of the hurricane.

Democrats suggest they have been given ammunition for their criticism by seemingly insensitive remarks of some Republicans.

These include House Speaker Dennis Hastert, R-Ill., questioning whether rebuilding New Orleans was worth the cost; comments by Barbara Bush, the president's mother, that "underprivileged" people would be better off in the Houston Astrodome; and a suggestion by Sen. Rick Santorum, R-Pa., that people who do not heed future evacuation warnings may need to be penalized.

In the first government estimate of Katrina's economic impact, the bipartisan Congressional Budget Office said the damage seemed likely to reduce employment by 400,000 in coming months and to trim economic growth by as much as a full percentage point in the second half of the year. The impact should be temporary, with gasoline prices declining and consumer spending rebounding, said the assessment obtained by The Associated Press.

Bush is expected to return to the region, but the White House would not say when. Separately, first lady Laura Bush planned to travel to Mississippi on Thursday, the same day Cheney heads to the Gulf states.

The Associated Press contributed to this report.