He said that faced with time constraints imposed by congress -- which gave a strict deadline for the new federalized screener system to be in place -- the Department of Homeland Security turned to the private sector to get the background checks completed on time.
"We couldn't possibly get the FBI and others to do that," he told lawmakers on the new House Homeland Security Committee, "so we had to engage companies within the private sector."
He said the companies responsible might face financial penalties.
Ridge added that the time constraints were no excuse, and that the chief of the Transportation Security Administration would look into the matter.
"I'm not trying to condone the sloppiness or the inaccuracy of the work that was done," he said. "We saw that ourselves, and (TSA chief) Admiral Loy is taking the necessary corrective action."
He said that the companies had initially run a "name-only" background check. Chris Rhatigan, a spokeswoman for the TSA acknowledged there was "still ... some cleaning up to do" on the background check process.
"Certainly there are a few people -- among all the thousands and thousands we checked -- who might have slipped through the net," she told United Press International.
Reports in The Washington Post last week suggested that dozens of screeners at Los Angeles International Airport, JFK in New York, Dulles in suburban Virginia and perhaps other major airports had been hired despite having criminal records, or without fully completing the background check process.
Ridge said the Office of Personnel Management in the White House was now conducting more thorough background checks, but cautioned the process would be lengthy, because of the 55,000 screeners involved. He added that the companies responsible would be financially penalized.
"We've had some questions with regard to the performance of ... one of the companies," he said, adding, "We have withheld quite a bit of money from one of these contractors."
Rhatigan told UPI that all the contracts the TSA has with private companies are kept continuously under detailed review.
Congress established the TSA after the terrorist attacks on Sept. 11, 2001, to ensure that a more skilled, better-paid and more highly educated workforce would take over security screening at airports. Like all other aviation workers who have access to non-public areas, TSA screeners are supposed to pass thorough criminal history checks before they start.