"I talked to the President this morning and sent him my letter of resignation and will make it effective on the confirmation of my successor," Lehman, 44, told reporters at a Pentagon news conference. He said one major reason for leaving was to spend more time with his wife and three children, who are 3, 7 and 9. "I want to spend more time with them as they grow up," Lehman said.
Lehman, a member of a wealthy Philadelphia family, promptly sought to squelch rumors that he was resigning to run for political office or to manage the 1988 presidential campaign of Vice President Bush, as published reports had suggested last year.
"I'm not going to be running for office in the foreseeable future and will not be running anyone's campaign," Lehman said. But he did not rule out seeking political office in the "long term."
Lehman said it was a "good time" for his departure after six years in the post "and putting into place the 600-ship Navy." Both the Navy and its infantry arm, the Marine Corps, are "in good shape," he said.
The administration has added 75 ships to the Navy, he said, and the 600th ship - a key Reagan goal - is to be launched in fiscal 1989.
Lehman said he would continue to make his home in the Washington suburb of McLean, Va., and would prefer "to get into an executive job. It is not my intention to go to work in the defense industry," he said. "But when you are looking for a job, you don't rule out anything."
He said that he expected an announcement soon on his replacement and that he would stay on the job until a successor is confirmed by the Senate and takes office.
Pentagon officials said that Reagan was expected to nominate Webb as Lehman's successor and that a White House announcement was expected this week. The appointment requires Senate confirmation.
Webb, a novelist who was awarded the Navy Cross, the Silver Star, two Bronze Stars and two Purple Hearts as a Marine infantry officer during the
Vietnam War, resigned about 10 days ago as assistant defense secretary for reserve affairs. He had planned to write another novel.
One of his books, Fields of Fire, was about the Vietnam War. Another, A Country Such As This, was nominated for the Pulitzer Prize and the PEN/ Faulkner Award.
Pentagon spokesman Robert Sims disclosed Thursday that Lehman had told Weinberger Feb. 6 of his intention to resign.
Despite predictions to the contrary from some congressional and private budget analysts, Lehman said he thought that future U.S. military budgets would rise slightly and would be adequate to supply manpower and aircraft for a 600-ship Navy.
But he warned that the United States must keep building new warships, even if a future president and Congress decide to cut back from the 600-ship level. ''Sixty percent of the Navy's budget goes to operating the fleet now," he said.
"If presidents in the future find that the threat is less . . . that we can give up our commitments in the Atlantic or the Pacific and we can do with a smaller Navy, then what you do is early retire the older ships.
"You don't eat the seed corn by not building the new ships."