"I'm not a hurricane expert," Chertoff said several times in responding to criticisms from members of a special House panel set up to investigate the dismal federal response to Katrina, which killed more than 1,200 people, flooded New Orleans and forced the evacuation of hundreds of thousands.
Chertoff, a former prosecutor and Justice Department official, took over the Homeland Security Department in February.
Lawmakers grilled Chertoff about why he stayed home Saturday before Katrina made landfall on Monday, why he made a previously scheduled trip to Atlanta on Tuesday, and why he didn't act more decisively to speed up the federal response.
Chertoff said he relied on former FEMA Director Michael Brown as the "battlefield commander" and focused his efforts on making sure FEMA had all the resources it needed. He said he stayed in telephone contact with the office while at home and during the trip to Atlanta.
"I don't think there was a lack of a sense of urgency," he said.
Chertoff's appearance came as weather forecasters kept a, the latest in a host of such storms, as it has grown into one of the most intense Atlantic hurricanes on record. Forecasters said it likely will strike the east coast of Florida with devastating winds by late in the week.
Most of the blame for the federal response to Katrina has fallen on Brown, who resigned last month after Chertoff removed him from direct responsibility for Katrina relief and recovery efforts.
in Louisiana for the slow response to Katrina when he testified before the committee last month. Chertoff disagreed.
"From my own experience, I don't endorse those views," he said.
After the levees broke in New Orleans, Chertoff said he became increasingly frustrated with the federal response and decided by the end of the first week to replace Brown with Coast Guard Vice Admiral Thad Allen. A week later, he relieved Brown of his duties and ordered him back to Washington.
Wednesday's hearing provided the first opportunity for lawmakers to question Chertoff directly about his role in the response. FEMA was an independent agency before it was folded into the Department of Homeland Security when it was created after the Sept. 11 terrorist attacks.
The investigation is being conducted by a special committee appointed by House GOP leaders. Democratic leaders, insisting on an independent investigation, have refused to cooperate in what they contend is a too-soft probe of the Bush administration by GOP lawmakers.
Several Democratic congressmen from the affected areas have attended the hearings and questioned witnesses. They were joined Wednesday by Rep. Cynthia McKinney, D-Ga., who blasted what she called a lack of leadership in the Bush administration's response to Katrina.
Rep. Henry Bonilla, R-Texas, objected when McKinney asked Chertoff why he should not be charged with negligent homicide because of the federal response.
When questions "are over the top and not constructive, I don't believe the secretary should waste his time by answering," Bonilla said.
Chertoff did answer, however, declaring the President Bush "was deeply and personally engaged in the process from before the hurricane; I was deeply and personally involved in the process from before the hurricane."
Earlier, Chertoff told the committee that FEMA was overwhelmed by Katrina and must be retooled to improve preparation and response to natural disasters.
"There are many things that did not work well with the response," Chertoff said, adding later, "We are not where we need to be as a nation in the area of preparedness."
Chertoff said Katrina demonstrated that FEMA's system for moving supplies into disaster areas is not adequate and that communications systems must be made to work even in the worst disasters. He said the agency also must learn how to identify issues and target resources when state and local officials are overwhelmed by a storm.