The House Armed Services Investigations Subcommittee yesterday warned the Carter administration against buying a German gun for the U.S. Army's new tank to improve chances of selling West Germany an airborne command plane.

"There appears to be a curious but nonetheless pervasive interrelationship" between the two weapons, the subcommittee complined in releasing a 15 page report on the XM-1 tank the Army is building for the 1980s. The total cost of the program is expected to be about $5 billion.

The Army last summer picked Chrysler to build the XM-1 tank. But what kind of gun should go on it is still at issue. The contest is between the U.S. rifle bore 105 mm, the British riflebore 120 mm, and the West German smoothbore 120 mm tank gun.

Although there is no official U.S.West German agreement of the gun to go on the XM-1, the committee said that "leading members of the German Bundestag" have said that failure to buy the German gun would mean that Germany would not buy the U.S. Air Force's airborne warning and command (AWCS) aircraft, which cost about $120 million.

Chairman Samuel S. Stratton (DN.Y.) said his subcommittee report is intended to be "a clear warning" to the Carter administration to choose the XM-1 tank gun strictly on military, "not political considerations."

The subcommittee report said tests to date have shown that the 105 mm gun would be "more than adequate against all tanks on the battlefield today." The Army is scheduled to finish its final its final testing of the three guns by the end of December.

In other sections of the report, the subcommittee criticized the way the Army contracted for the XM-1 tank and said it was "gravely disturbed" to learn of the worried the Army had with the turbine engine for the tank.

"Under the circustances," the subcommittee said, "the Army should consider continued development of a diesel backup engine for the XM-1."

Only after the Army had awarded a $196.4 million contract to Chrysler to develop the XM-1 tank, the committee complained, did the Army start negotiatiog with the company to add another $29.6 million to the contract to finance further tests of the turbine engine.

"Last fall," the report said, "the committee was assured that the turbine was not a high risk item" and no reference was made to the need for additional testing.