By Doina Chiacu

WASHINGTON (Reuters) - The new leader of the Transportation Security Administration said on Wednesday his top priority would be to close security gaps at airport checkpoints where an internal report showed 96 percent of undercover tests failed.

Peter Neffenger, the agency's new administrator, told a congressional panel that front-line TSA employees would be trained by September to avoid the pitfalls that led to those failures.

"My highest priority is to ensure solutions to the recent covert testing failures," Neffenger said.

Lawmakers opened the U.S. House of Representatives hearing with references to a Department of Homeland Security report that found TSA airport screeners did not detect banned weapons in 67 of 70 tests at dozens of airport checkpoints.

"These findings shatter public confidence," said Republican Michael McCaul, chairman of the House Homeland Security Committee.

"What are you planning to do as the new TSA administrator to address this enormous failure?" McCaul asked.

The findings in an internal report by the DHS inspector general were disclosed last month by news media, prompting criticism that the TSA was emphasizing speed over security.

Homeland Security Secretary Jeh Johnson reassigned the acting TSA administrator last month and announced steps to improve security at airports.

Neffenger said the agency would also improve its expedited screening procedures and tighten oversight of security badges.

The former Coast Guard vice admiral, who has been in the job four weeks, takes over an agency struggling with poor efficiency and low morale.

The committee's senior Democrat, U.S. Representative Bennie Thompson, cited multiple breaches caused by airport employees exploiting security gaps and personnel problems within the agency.

"TSA is plagued with very low morale and an extremely high turnover rate," Thompson said.

Representative John Katko cited control over who gets access to airport's secure areas as a "major, gaping hole" in airport security nationwide.

The New York Republican sponsored legislation to tighten security standards for airport employees after recent incidents involving the trafficking of drugs and guns by employees.

(Reporting by Doina Chiacu; Editing by Alden Bentley and Bill Rigby)