The head of the government agency charged with airport security plans to step down, his spokesman said Friday.

Transportation Security Administration chief David Stone (search) will leave the job in June, said spokesman Mark Hatfield, who did not provide a reason for the move. No replacement was announced.

Stone, a retired Coast Guard admiral, is the third TSA chief since the agency was created in the aftermath of the Sept. 11 terror attacks. He was preceded by James Loy (search), former commandant of the Coast Guard, and John Magaw (search), former head of the Secret Service. Stone's 16-month tenure as TSA chief was the longest.

"He did a good job," said Rep. John Mica, R-Fla., and chairman of the House aviation subcommittee. "I worked well with Admiral Stone."

Mica, though, has criticized the TSA for being a "Soviet-style bureaucracy" with too many airport screeners who don't perform well enough detecting explosives and dangerous items on passengers. He wants to see the agency transformed so that private companies take over airport screening and the TSA simply oversees the private companies.

"TSA did a great job in putting an army of 48,000 screeners together, but then when you stand back and look at the results, the performance is just not acceptable," Mica said.

He said he's concerned that it will take time to replace Stone, which will cost an opportunity to restructure the TSA.

Stone is leaving as the new Homeland Security secretary, Michael Chertoff (search), is reviewing the structure of the entire organization, which includes TSA.