After four years of trying to reduce federal employment, the Reagan administration today finds 77,000 more more full-time civil servants on the payroll than it did when the president took office, Rep. Patricia Schroeder (D-Colo.) reports.

Schroeder, who chairs a subcommittee of the House Post Office-Civil Service Committee, says that layoffs in the departments of Health and Human Services, Labor, Transportation, Energy and Housing and Urban Development and the Office of Personnel Management have been more than offset by increased civilian hiring by the Defense, Justice and Agriculture departments and the U.S. Postal Service.

Schroeder and the Office of Personnel Management have been involved for years in a dispute over civil service body counts. She said her statistics come from OPM, where they were compiled from official records. But OPM says it actually uses a different system, called "full-time equivalents," to interpret the size of the payroll.

Under the equivalents system the government counts the total number of hours worked in a year and divides them by 2,087 hours (the civil service work year) to get a full-time total.

Patrick Korten, OPM's executive assistant director for policy and communication, said yesterday that President Reagan pledged to "reduce that part of government that interferes with people's lives, which he did, and to strengthen the Defense establishment, which had slipped badly in the 1970s."

By OPM's reckoning, the number of full-time equivalent positions is down 78,000, excluding the Defense Department. Counting Defense, the number of equivalents has increased by 10,000.

Korten said the Defense Department has been exempt from civilian personnel restrictions for the past year, by order of Congress. He said that Schroeder, a member of the House Armed Services Committee, voted for that exemption.

"If she wants to do something about it," he said, "she can. It is time for Ms. Schroeder to put up or shut up."

President Reagan's first official act in January 1981 was to slap a hiring freeze, retroactive to November 1980, on federal agencies. The courts eventually ruled that he did not have legal authority to cancel job promises that had been made to an estimated 20,000 applicants before he actually took the oath of office.

In the first three years of the Reagan administration a number of federal agencies with domestic and welfare missions were hit by a series of reductions-in-force.

Many of the employes who were fired were part-timers. About 9,000 workers in this area lost their jobs because of the RIFs. Many more workers, mostly those with little seniority, were downgraded or moved to other jobs because of the ripple effect of the RIFs.

But between 1981 and 1985, Schroeder says, the Army hired 28,000 new civilian workers, Navy an extra 22,000 and the Air Force over 13,000. State and Treasury also expanded, and the semi-independent U.S. Postal Service, the largest federal agency, hired more than 31,000 new employes.

Schroeder said there were 2,487,017 full-time permanent federal employes by January of this year, up from 2,410,313 four years earlier.