The report, to be released in full on Wednesday, also says that emergency planners failed to act on warnings before the Hurricane laid waste to New Orleans and the surrounding region last August.
"In many respects, our report is a litany of mistakes, misjudgements, lapses and absurdities all cascading together, blinding us to what was coming and hobbling any collective effort to respond," said the lawmakers.
"Our investigation revealed that Katrina was a national failure, an abdication of the most solemn obligation to provide for the common welfare," they added.
"At every level -- individual, corporate, philanthropic and governmental -- we failed to meet the challenge that was Katrina."
Media reports say the full 600-page report will also criticise the administration from President George W Bush down.
The advance report said that the Federal Emergency Management Agency (FEMA), part of the Homeland Security Department, knew more than two days in advance that 75 percent of New Orleans was probably going to be flooded.
It criticised Homeland Security Secretary Michael Chertoff for not giving a strong enough alarm.
FEMA overhaul
Pre-empting the report, Mr Chertoff unveiled a major overhaul of FEMA but also defended his department from the mounting attacks.
He said FEMA would upgrade its alert procedure and add hundreds of new staff, to allow it to respond more quickly to catastrophes.
"As the secretary of homeland security, I am accountable and I accept responsibility for the performance of the entire department," he told a conference of emergency management officials.
Mr Chertoff rejected accusations from a former FEMA chief that the Homeland Security Department had become obsessed with the US "war on terror" and had not taken natural disasters seriously.
"I unequivocally and strongly reject this attempt to drive a wedge between our concerns about terrorism and our concerns about natural disasters," he said.
House Democrats, who boycotted formal participation in the Katrina investigation, have called for Mr Chertoff's resignation.
Fraud costs victims millions of dollars
The Bush administration also faced scathing criticism from a Congress watchdog which said millions of dollars in Katrina aid was given to people who provided false identities and addresses.
The Government Accountability Office (GAO) said although the US government has spent billions of dollars on aid and reconstruction efforts much of that money has been misplaced.
Almost 900,000 of the 2.5 million requests for direct financial aid may have been false, according to GAO investigators.
FEMA had US$5.4 billion (A$7.33 billion) in emergency cash and much of that was given in US$2,000 dollars direct debit cards for victims.
In a study on a sample of 248 requests, GAO investigators found that 165 had given false social security numbers -- some of which were allotted to dead people or had been made up.
Of 200 who requested aid for a damaged home, 80 gave addresses that do not exist.
"In total, the case study registrants of whom we conducted investigations have collected hundreds of thousands of dollars in payments based on potentially fraudulent activities," said GAO investigator Gregory Kutz, who gave testimony to a Senate inquiry.
Mr Kutz did not give a figure for the total amount believed lost to fraud. He said the GAO inquiry was still going on.
Finding new homes
Meanwhile, thousands of people who lost their homes in the disaster were packing up their belongings again on Monday after the federal government stopped paying their hotel bills.
While FEMA will continue to provide financial assistance to the bulk of the 12,600 families who still have not found permanent housing, it stopped making direct payments to the hotels.
"We're going to have thousands of homeless people today," Tracie
Washington, a civil rights attorney who filed an unsuccessful lawsuit to force FEMA to continue to pay the bills, told AFP.
Ms Washington also said that FEMA had failed to deliver trailers promised to people living in the hotels.
In New Orleans, hotel lobbies of the historic French Quarter were filled with the bags of people who were trying to figure out where to go next.
Casetta Williams, 40, watched her brother pack up for a dilapidated hotel on the edge of town after he was evicted from his hotel downtown.
"Quite a few people were evicted today," she told AFP.
"I saw at lot of people packing up and they were leaving out. My heart went out to them because a lot of people really don't have anywhere to go. A lot of them have gotten work and now they have to let go out their jobs because they don't have anywhere to live," she said.