Sources within the U.S. Senate released documents to CBS News Wednesday that include a devastating assessment of the Federal Emergency Management Agency conducted at Brown's request in March 2005.
The study, done by the MITRE Corp., showed FEMA to be totally dysfunctional, reports CBS News correspondent Mary Hager.
Brown's stance, in a letter obtained Wednesday by The Associated Press, follows senators' complaints that the White House is refusing to answer questions or release documents about advice given to Mr. Bush concerning the Aug. 29 storm.
Brown quit as director of the Federal Emergency Management Agency days after Katrina struck. He left the federal payroll Nov. 2.
In a Feb. 6 letter to White House counsel Harriet Miers, Brown's lawyer wrote that Brown continues to respect Bush and his "presidential prerogative" to get candid and confidential advice from top aides.
The letter from Andrew W. Lester also says Brown no longer can rely on being included in that protection because he is a private citizen.
"Unless there is specific direction otherwise from the president, including an assurance the president will provide a legal defense to Mr. Brown if he refuses to testify as to these matters, Mr. Brown will testify if asked about particular communications," the lawyer wrote.
Brown's desire "is that all facts be made public."
Messages left with the White House were not immediately returned Wednesday.
The report Brown requested last March depicted FEMA as disorganized and unprepared, Hager adds. Roles and responsibilities with the agency's headquarters' in general, and staffers in particular, were "unclear or redundant," according to the report.
Two weeks ago, Mr. Bush defended his administration's stance on withholding some information, saying that providing all the material would chill the ability of presidential advisers to speak freely. The White House has given thousands of documents about the storm response to Senate investigators.
Brown is set to testify Friday at a Senate inquiry of the slow government response to Katrina.