Ellen Howe, a spokeswoman for the T.S.A., said Monday that the agency has fired 465 officers for theft since the spring of 2003. That is “a minuscule fraction of the work force,” she said. She also said incidents were down sharply. In 2005, she said, the agency paid $3 million in claims for missing possessions or damaged bags. “This year it has been less than $1 million,” she said.