Washington ? The political struggle unleashed in Washington by the government’s response to Hurricane Katrina intensified Wednesday, with the congressional Republican leadership promising a joint House-Senate investigation into what went wrong as Democrats demanded the creation of an independent commission of inquiry.

Senate leadership aides said the joint panel would have the power to subpoena witnesses, but few other details were offered on the scope of its investigation or when it would begin.

Leaders of both parties insisted their primary focus remained aiding victims of the disaster, and they promised quick action on a $51.8 billion emergency aid package the White House proposed Wednesday. Congress earlier approved $10.5 billion in aid.

But partisan warfare was in full view on Capitol Hill, with Democratic leaders sharpening their attacks on the administration’s handling of the crisis as they sensed a rare opportunity to paint as inept the Republicans who control every lever of government in Washington.

In an unusually harsh attack on a president in a time of crisis, Sen. Minority Leader Harry Reid, D-Nev., said an investigation into the government’s response should ask, among other things, whether Bush’s absence from Washington – he was vacationing at his Texas ranch when the hurricane struck – impeded the federal government’s response to the disaster.

“How much time did the president spend dealing with this emerging crisis while he was on vacation?” Reid asked in a letter to Sen. Susan Collins, R-Maine., chairwoman of the Senate Homeland Security and Governmental Affairs committee.

“Did the fact that he was outside of Washington, D.C., have any effect on the federal government’s response?” Reid asked.

Responding to the attacks, congressional GOP leaders moved aggressively to take control of a political situation that threatened to derail Bush’s second-term legislative agenda and put Republicans running for re-election in vulnerable districts at risk next year.

Speaker of the House J. Dennis Hastert, R-Ill., and Senate Majority Leader Bill Frist ,R-Tenn., told reporters that their chambers would work together to determine why the response to Hurricane Katrina by all levels of government appeared to be inadequate. No Democrats were present at the announcement.

“We all agree that in many areas, the official response to Hurricane Katrina was unacceptable at the local, state and federal levels,” Frist said.

He said senior senators would serve on the committee, which would have until Feb. 15 to present its findings to the Congress.

“America deserves answers,” Frist said.

Shortly after the announcement, Reid said in a statement, “Democrats strongly prefer that the response to Hurricane Katrina be investigated by a commission of independent experts like the 9-11 commission.”

Having a Republican administration investigated “by a Republican-controlled Congress is like having a pitcher call his own balls and strikes,” Reid said.

But one senior GOP leadership aide, who requested anonymity, said Congress had a responsibility to “step up and face our responsibilities, not to shirk them” by shifting an investigation to an outside body.