Homeland Security Secretary Michael Chertoff acknowledged yesterday that Hurricane Katrina "overwhelmed" the Federal Emergency Management Agency and exposed major flaws in the nation's preparations for terrorism and natural disasters, but contradicted accounts by former FEMA director Michael D. Brown about his department's handling of the Aug. 29 storm.

Appearing for the first time before a House panel investigating the government's heavily criticized response, Chertoff vowed to "re-engineer" U.S. preparedness after the storm that killed more than 1,200 people and devastated New Orleans and the Gulf Coast. But he also blamed Brown and FEMA leaders, saying, "We certainly have to fill out the ranks of FEMA in terms of its senior level with experienced staff who can deal with all of the elements" of its mission.

Chertoff rebutted lawmakers' questions about why he worked from home Aug. 27, two days before the Category 4 storm hit, why he made a previously scheduled trip to Atlanta on Aug. 30, and why President Bush stayed at his Texas ranch until Aug. 31. "I don't think there was a sense of a lack of urgency," Chertoff said.

Instead, the secretary expressed growing frustration at days of conflicting reports from the scene, as well as the government's failure to speed relief to thousands of victims at the Louisiana Superdome in New Orleans or to rescue residents by air or boat.

"I knew I became more involved in operational matters than I would normally expect to be or want to be, given the fact that I had a battlefield commander on the ground," Chertoff said, referring to Brown. "I am not a hurricane expert. I've got to rely on people to execute the details of the plan."

Today, Marty Bahamonde, the only FEMA staff member in New Orleans when Katrina struck, is also expected to provide testimony contradicting previous statements by Brown and others. Susan Collins (R-Maine), chairman of a Senate Katrina investigation, said Bahamonde will present a detailed accounting of the "increasingly dire messages and phone calls" sent to Bush officials.

"More than any other person we've interviewed, he can give us an account of what really happened and who really knew about it and . . . why there wasn't more of a response," Collins said.

Two sources close to the Senate investigation said Bahamonde's testimony raises questions about why Chertoff and the White House did not receive his messages or learn the situation from photographs taken during a helicopter tour of New Orleans late Aug. 29, the day the city's levees were breached.

Bahamonde, a career employee, was the only FEMA staff member at the Superdome before the storm, Collins said, although Brown testified that the agency positioned about a dozen people there.

The hearings come amid a quickening pace of revelations by House, Senate and administration inquiries into confusion about roles among FEMA and Homeland Security officials under a new national response plan, conflicting accounts by those officials and FEMA's continuing struggles to provide aid for 1.6 million registered storm victims.

Seeking to regain control of the agenda of the department he took over just eight months ago, Chertoff thanked Congress for passing a $31 billion department spending bill that speeds the Bush administration's plans to further reorganize FEMA by transferring away its planning and preparedness offices into a new directorate.

State emergency managers and some critics in Congress say FEMA was crippled after the formerly independent agency was folded into the department after the Sept. 11, 2001, attacks.

Instead, Chertoff denied Brown's assertions, made last month to the House panel, that department budget and personnel cuts led to "the emaciation of FEMA." Chertoff said that from 2001 to 2005, FEMA's "core" budget grew 28 percent, to $447 million, and its staff 19 percent, to 2,445.

With support from department agencies such as the Coast Guard, Chertoff said, "FEMA has better resources, and . . . it brings more to the table now than it did in the previous five, six, seven years."

If the department fell down, it was "largely in the area of planning" for ultra-catastrophes, he said, which will be consolidated.

Brown testified that he pressed the White House to urge "dysfunctional" Louisiana and New Orleans leaders to order mandatory evacuations earlier before the storm hit. But Chertoff said, "I did not have a problem dealing with state and local officials."

He added, "Let me put it this way: Michael Brown didn't call me. I didn't speak to him prior to Sunday [Aug. 28] and have him tell me that he was having a problem with the governors."

Chertoff said he was unable to reach Brown the day after the storm hit until nearly 8 p.m.

"We now know that [FEMA's] capabilities were overwhelmed by the magnitude of the storm," he said.

Rep. Thomas M. Davis III (R-Va.), chairman of the House investigation, said that despite criticism of FEMA and Brown, Chertoff and his department "have primary responsibility for managing the national response to a catastrophic disaster."

Rep. William J. Jefferson (La.), one of four Democrats who participated in the GOP hearing despite a boycott by party leaders who are demanding an independent commission, called Chertoff "overconfident." The hearing, he said, "further confirms my belief that [FEMA] should have a Cabinet-level position" equal to the department.

Staff writers William Branigin and Ceci Connolly and researcher Don Pohlman contributed to this report.

Homeland Security chief Michael Chertoff testifies before the House panel investigating the government's response.