The number of political appointees has nearly doubled at four of the government's management agencies since the Reagan administration took office, while the number of their civil servants has been trimmed by more than 20 percent, a House subcommittee staff has found.

Using the "Plum Book" (otherwise known as "Policy and Supporting Positions"), the staff of the Post Office and Civil Service subcommittee on civil service determined that the number of political slots at the Office of Management and Budget, the General Services Administration, the Office of Personnel Management and the Merit Systems Protection Board increased from 86 in October 1980 to 127 in October 1984 -- a 47.7 percent increase.

At the same time, the staff said, the number of civil servants at those agencies dropped by 21.1 percent. The GSA lost 8,013 employes; OPM, 1,927; OMB, 35, and MSPB, 13.

Across the government, the number of political appointees increased about 4 percent, from 3,195 employes to 3,311, while the number of civil servants increased by about 1 percent -- from 2,137,730 in December 1980 to 2,159,221 in December 1984 -- when the Defense Department's civilian workers and the U.S. Postal Service are included. The administration usually excludes those workers when it reports how it has trimmed the federal work force. When those employes are excluded, the number of civil servants dropped 6.35 percent, from 1,166,731 in 1980 to 1,092,631 in 1984.

Referring to the four management agencies, the head of the subcommittee, Rep. Patricia Schroeder (D-Colo.), said, "These agencies are the ones entrusted with ensuring that the government operates efficiently and productively. I really worry when I see this administration getting rid of career workers and bringing on large numbers of inexperienced political appointees."

GSA spokesman Patrick H. McKelvey said the House member's charge sounded "like just another cheap shot" and said he'd look into the numbers to see if "it amounts to anything." Several GSA officials, however, said that the agency now has nine more political slots than reported in the Plum Book. Gregory Knott, GSA's personnel chief, acknowledged that the last GSA administrator in the Carter administration, Rowland Freeman, preferred to fill top jobs with career civil servants, while the Reagan administration prefers to fill them with political employes.

Patrick S. Korten, OPM's chief spokesman, said his agency needed the extra political appointees because it was transformed from the "mechanical" Civil Service Commission in 1979 to "an integral part of the management team of the federal government" under President Reagan.

"This is all smoke," Korten said. "The Democrats have their own little drumbeat going."

Civil service employment at OPM dropped, Korten said, because the agency eliminated a grants program, "trimmed a couple of layers of management that didn't need to be there and did some things more efficiently. When we reduce 2,000 or so employes and bring on 15 political employes, I'm afraid I don't see any comparison in terms of magnitude."

OMB spokesman Steven R. Tupper said he was unaware of a growth in political appointees and had no comment.