Transportation Secretary Norman Mineta is calling it quits.

Mineta, who has been the only transportation secretary in the George W. Bush administration, submitted a letter to the president on Tuesday announcing his resignation. White House spokesman Tony Snow announced it Friday morning at a White House briefing. According to the letter, Mineta's resignation will be effective July 7.

"While there remains more to be done - a job such as this is never truly completed - I can assure you that the Department of Transportation is well-positioned, with highly competent and dedicated people you brought in as well as the civil service workforce, to fulfill the mission that you and the Congress advance in the years ahead," Mineta wrote in his letter to Bush.

Mineta is the only Democrat who has served in Bush's cabinet after having been the Commerce secretary during the Clinton administration and before that a congressman representing San Jose, Calif.

Mineta, 74, outlasted most expectations about his time at the head of the Department of Transportation. Hobbled by health problems earlier in his term, he has by all appearances recovered and has maintained a busy public schedule in recent months.

Although Mineta's departure comes shortly after a spate of other high-profile administration officials have left during a second-term White House reorganization, White House press secretary Tony Snow told reporters Mineta was leaving on his own.

"He's not being pushed out," Snow said at Friday's briefing with reporters.

Snow said Bush will not go out of his way to appoint another Democrat to head the DOT.

"At this point, you look for the best people you can get," Snow said.

DOT spokesman Robert Johnson said Mineta, who was a Lockheed Martin executive immediately after his congressional service, has plans in place for what is next but is not ready to announce them.

"Norm Mineta always has a plan," Johnson said. "With regard to decisions he's making and when he'll make them, he's choosing at this time to make any announcements regarding that after July 7."

Angela Greiling Keane