A behind-the-scenes battle is being waged in the Reagan camp against the prospective appointment of Frank C. Carlucci, deputy director of the Central Intelligence Agency, as deputy secretary of defense.

Carlucci's critics contend he is not conservative enough and does not know the defense industry he would oversee in the Pentagon's No. 2 job. Some Reaganites are trying to sell the president-elect instead on Ruben F. Mettler, board chairman and chief executive officer of TRW Inc.

Carlucci is aware of the battle but is staying out of it. He is telling friends he is willing to serve as deputy to his old friend and Reagan's choice for defense secretary, Caspar W. Weinberger, but will not be broken-hearted if he is passed over.

One of Carlucci's critics on the Reagan transition team conceded yesterday that Weinberger could insist on Carlucci and get him, but said this would cost the new Republican president support among conservatives in Congress who would shape future defense programs to their own liking if disillusioned with the new Pentagon team.

Another argument being made against Carlucci in transition team screening sessions, which one insider yesterday termed "really rough," is that with Weinberger and Carlucci, there would be two managers with a reputation for budget cutting at the top of the Pentagon. Neither would have balancing expertise in defense procurement or military policy, critics charge, at a time the Pentagon would be spending record amounts of money on readiness and modernization.

Mettler was part of the "blue ribbon" panel which reviewed Pentagon practices in 1969 for then-Defense Secretary Melvin R. Laird, with an eye to improving efficiency. Mettler also headed a presidential panel in 1970 which recommended "increased emphasis on research and development for national security purposes, even at the expense of current military hardware procurement if necessary."

The TRW chief executive said through a spokesman yesterday that he has not been contacted by the Reagan team about the Pentagon post "and consequently has nothing to say."

The TRW complex Mettler heads has offices in several states. Its sales to the U.S. government in 1979 totaled $872 million, or 19 percent of its total sales of $4.56 billion. The Pentagon is a big customer for TRW electronic equipment.

While the Carlucci appointment was creating transition controversy, insiders said there was comparative harmony in discussing the leading candidate for at least one Pentagon job -- secretary of the Army. John O. Marsh Jr., former Democratic congressman from Virginia's 7th District and White House counselor to President Ford, has a big edge, they said. Ford is pushing marsh for the post.

Rep. Robin Beard (R-Tenn.), who was sounded out about becoming Army secretary, agreed yesterday that Marsh looked certain. Beard added that Vice President-elect George Bush had told him the Reagan team did not want to risk losing Beard's congressional seat to a Democrat by appointing him Army secretary. Beard wrested Tennessee's 6th District seat from the Democrats in 1972.

The main competition for secretary of the Navy pits long-time Reaganite Robert D. Nesen against John Elhman, former deputy director of the Arms Control and Disarmament Agency and currently president of a Washington management firm.

Reached at his Ventura County, Calif., Cadillac-Oldsmobile dealership yesterday, Nesen said: "Yes, there have been discussions" with the Reagan transition team about becoming Navy Secretary. "I'm interested, but there's nothing definite."

Nesen has considerable political leverage, given the face he has been active in California Republican politics for 30 years, knows both Reagan and Weinberger, and headed the state's delegation to the GOP convention this year. He served as assistant secretary of the Navy 1972-74 under President Nixon. "I'm a young 63," Nesen quipped.

Lehman, 38, a former Navy pilot, said Navy secretary is the only job in the administration he wants, or would take. He is president of the Abington Corp.

Still far from settled are what job William Van Cleave, Reagan's defense adviser, will end up with and who will be secretary of the Air Force, transition sources said yesterday.