The Homeland Security Department was warned a day before Hurricane Katrina hit that the storm's surge could breach levees and leave New Orleans flooded for weeks or months, documents released Monday show.

An Aug. 28 report by the department's National Infrastructure Simulation and Analysis Center concluded that a Category 4 or 5 hurricane would cause severe damage in the city, including power outages and a direct economic hit of up to $10 billion for the first week.

"Overall, the impacts described herein are conservative," stated the report, which was sent to Homeland Security's office for infrastructure protection.

"Any storm rated Category 4 or greater ... will likely lead to severe flooding and/or levee breaching, leaving the New Orleans metro area submerged for weeks or months," said the report, which was released by a Senate panel examining the government's breakdown in responding to Katrina.

The documents are the latest indication that the federal government knew beforehand of the catastrophic damage that a storm of Katrina's magnitude could cause.

Katrina slammed into the Gulf Coast as a Category 4 storm on Aug. 29. Some weather experts, however, believe it had decreased to a Category 3 or even Category 2 storm by the time it reached New Orleans.

In 2004, Homeland Security and the Federal Emergency Management Agency ran an exercise called "Hurricane Pam" that provided a dire prediction about a Category 3 hurricane hitting New Orleans. It found, among other things, that flood waters would surge over levees, creating "a catastrophic mass casualty/mass evacuation" and leaving drainage pumps crippled for up to six months.

The Bush administration has been lambasted for its lackluster response to Katrina and its aftermath, including criticism that the government should have known that a hurricane of that strength posed a danger to the area's levees and was unprepared to cope with it.

Homeland Security spokesman Russ Knocke said he was not familiar with the documents but that the levees situation likely was one reason the government urged an evacuation of New Orleans before the storm hit.

"We're in the process of participating in a large after-action report," Knocke said. "We're deeply committed to finding out what worked and didn't work, and apply those lessons learned going forward."

Shortly after the disaster, President Bush said, "I don't think anybody anticipated the breach of the levees." He later clarified his remarks, saying his comment was meant to suggest that there had been a false sense of relief that the levees had held when the storm passed, only to break a few hours later.

The documents were released by the Senate Homeland Security and Governmental Affairs Committee on the eve of a hearing about Hurricane Pam and other government preparations for catastrophes. Pam, a so-called "tabletop" exercise that began in July 2004, focused planners on a mock hurricane that produced more than 20 inches of rain and 14 tornadoes.

As part of the Pam project, federal and state officials working with government contractors also estimated that plans to move victims from disaster areas were only "10 percent done," the documents show.

"If you think soup lines in the Depression were long, wait 'til you see lines at these collection point (sic)," said one official, identified as U.S. Transportation Department regional emergency officer Don Day, in a briefing on July 29, 2005.

"We're at less than 10 percent done with this trans (sic) planning when you consider the buses and the people," Day said at the briefing, notes of which were given to the Senate committee by Innovative Emergency Management Inc. of Baton Rouge, the contractor hired by FEMA to conduct the exercise.