Ridge, in an interview with the Washington Post, declined to blame his successor, Michael Chertoff, or Michael Brown, who resigned as Federal Emergency Management Agency director after Katrina.
But he said the agency failed to put emergency plans into effect as Katrina approached.
"There just didn't seem to me to be any collaboration up front, any communication," he said. "You don't have to be a meteorologist to see a big red ball going to New Orleans to say, 'Oh, my God, this is going to be big.' Shouldn't you be over-prepared, rather than under-prepared?"
The interview was the former Pennsylvania governor's first public response to Katrina.