WASHINGTON — The new administrator of the beleaguered Transportation Security Administration said the agency would make several changes to security and screening procedures as part of an overhaul to address glaring lapses over the past few months.

Peter V. Neffenger, who took over the agency this month, said in an interview that the T.S.A. would retrain thousands of screeners to better detect weapons and other illegal items, scale back a program that allows people who have not signed up for background checks to use expedited security lines and more aggressively police airports’ oversight of security badges.

The agency has been on the defensive after disclosures in June of a report by the Inspector General’s Office of the Department of Homeland Security, first reported by ABC News, that found agents failed 67 of 70 security tests. In one such test, they did not spot undercover investigators’ passing through checkpoints with potential weapons. The findings prompted criticism by many former and current T.S.A. employees who said the agency emphasized moving passengers quickly through lines over security.

“Efficiency and getting people through airport security lines cannot be our sole reason that makes you take your eyes off the reason for the mission,” said Mr. Neffenger, a former Coast Guard vice admiral, who is to testify on Wednesday before the House Homeland Security Committee.