Chertoff acknowledged "many lapses" and said he accepted responsibility on Wednesday. He called the storm "one of the most difficult and traumatic experiences of my life".
Chertoff, on the job for one year on Wednesday, drew sharp criticism from both the Republican chairwoman and senior Democrat on the Senate Committee on Homeland Security and Governmental Affairs.
Senator Susan Collins, the panel's chairwoman, said the Department of Homeland Security's performance in responding to the hurricane "must be judged a failure".
She called it "late, uncertain and ineffective".
Senator Joseph Lieberman, the panel's top Democrat, criticised Chertoff for going to Atlanta for an unrelated conference on 30 August, the day after the storm roared ashore.
Lieberman said: "How could you go to bed that night (29 August) not knowing what was going on in New Orleans?"
Lieberman said that under Chertoff's oversight, disaster workers "ran around like Keystone cops, uncertain about what they were supposed to do or uncertain how to do it".
Michael Chertoff said Katrina was
traumatic for him
Collins told Chertoff "I remain perplexed" about his decision to designate Michael Brown, then chairman of the Federal Emergency Management Agency, as point man on co-ordinating the government's response to Katrina.
Brown, widely criticised for his performance, resigned under pressure soon after.
He later accused others in the administration, including White House officials and Chertoff, of dragging their feet and ignoring his warnings of widespread flooding in New Orleans after the storm hit.
Chertoff said there was "no reason to doubt his commitment".
"If I knew then what I know now about Mr Brown's agenda, I would have done something different."
"When I went to bed, it was my belief ... that actually the storm had not done the worst that could be imagined"
director of Homeland Security
He reiterated that he did not realise that levees or embankments in New Orleans had been breached on the day of the storm - despite Brown's claims to the contrary.
"When I went to bed, it was my belief ... that actually the storm had not done the worst that could be imagined."
A House inquiry titled "A Failure of Initiative," which was released on Wednesday, concluded that much of the death and suffering might have been avoided if the government had heeded lessons from the 2001 terror attacks and taken a more proactive stance toward disaster preparedness.