John F. Lehman Jr. is almost certain to become Ronald Reagan's secretary of the Navy, and former senator James L. Buckley has been penciled in as Air Force secretary on the new Pentagon team, sources said yesterday.

This skirmishing for sub-Cabinet spots at the Pentagon typifies what is going on all over Washington as candidates and their backers struggle to get a piece of the new action that becomes available with a change of administrations.

Getting as close as possible to the seat of power is the object of the game. The first step is to get your name in the Reagan transition team's in-basket, the second is to get on its list of possibles and the third is to get the job offer -- ideally from the president-elect himself.

All this has been going on for weeks now, and the lists of candidates for the top jobs at the Pentagon and other government departments have grown long, forcing the competitors to step up their lobbying, even though the Cabinet secretaries and Reagan with the help of his advisers, will make the selections in the end, not the transition teams on the East and West coasts.

At the Pentagon, William Van Cleave, Reagan's chief sifter of names and defense policy papers, sits in a temporary transition office on the Pentagon's prestigious E-ring, just a few doors away from the third-floor office of Defense Secretary Harold Brown. His in-basket is brimming.

Those insiders who will talk about who is in and who is out at the moment said yesterday that Lehman, 38-year-old president of the Abington Corp., a Washington-based international management consulting firm, has had the inside track for Navy secretary for so long that he seems a shoo-in.

Lehman, who attacked President Carter's defense policies while campaigning for Reagan, was more forthright about his ambitions yesterday than most of the players in the power game.

"I'm interested in becoming secretary of the Navy," said the former Navy pilot, who has championed the nuclear aircraft carriers Carter has opposed. "It's the only job I am interested in." Lehman's previous government service includes being deputy director of the Arms Control and Disarmament Agency under President Ford.

Buckley, the Republican conservative who was New York's senator and this year lost his bid for the Connecticut Senate seat being vacated by Democrat Abraham A. Ribicoff, also wants to be secretary of the Navy. But sources in the Reagan camp yesterday said that avid sailor Buckley will have to settle for becoming Air Force secretary if he wants to join the civilian hierarchy at the Pentagon. Environmentalists had looked at Buckley as an ideal candidate for interior secretary -- he has a sufficiently pro-environment record to satisfy them and seemed sufficiently conservative to suit Reagan. But Buckley has made the Pentagon list, the Reagan camp said.

The job of Army secretary is still wide open, sources said. Names on the list include Patrick Parker, former Pentagon "Whiz Kid" and currently professor at the Navy's post-graduate school in Monterey, Calif.; Washington lawyer Martin R. Hoffmann, Army secretary from 1975 to 1977; Rep. Robin Beard -R-Tenn.), a harsh critic of the All Volunteer Army, and William Brehm, who was Pentagon manpower chief from 1973 to 1976.

In pushing the candidacies of Hoffmann and Brehm, friends are contending that experience makes them the best bets to straighten out the manpower mess Beard and others have deplored in attacking the volunteer military.

Reagan has said that there is nothing wrong with the All Volunteer Force that pay and other benefits will not fix. He has opposed returning to the draft and is even against requiring young men to register. He is being pressed to cancel the scheduled January registration.

The Pentagon's International Security Affairs Office -- called "the little State Department" because it deals with foreign policy issues more than hardward -- has a long list of prospective directors. They include Van Cleave, sources said (even though his backers insist only a higher job like deputy secretary of defense would suit him), William Schneider, a defense specialist from the Hudson Institute with close ties to Rep. Jack Kemp (R-N.Y.), and William Kintner of the University of Pennsylvania.

For the technical job of directing the development and production of weapons -- Pentagon research and procurement chief -- the names of Van Cleave and Benjamin T. Plymale of Boeing Co. are among those on the list.

Although Reagan insiders said Caspar Weinberger remains the front-runner for secretary of defense, the former Nixon budget chief has raised some hackles among congressional hard-liners.

"He doesn't know anything about defense," Rep. Samuel S. Stratton (D-N.Y) complained yesterday. On top of that, continued Stratton, Weinberger is known as "a budget cutter" at a time the country wants the Pentagon budget increased.