Federal employment in metro Washington -- which has been losing about 1,000 U.S. jobs per month -- is down to 345,456. That is the lowest number of people on the government payroll here since 1975.

The downward trend in federal employment, which is expected to continue, could spell trouble for the Washington area, which relies heavily on the $775,245,000 monthly government payroll.

There has been a steady decline in the number of feds since President Reagan took office.

In January 1981 there were 366,678 federal government employes in metro Washington.

Last September, after summer hires had been removed from the payroll, the number of federal employes here was 352,681. The number dropped to 350,785 in October and to 347,889 by January. In February of this year there were 346,282 federal workers here, and that number declined to 345,456 in March, the latest figures available.

Since President Reagan took office, about 9,000 federal workers have been RIFfed -- fired for economy reasons -- including about 2,800 in this area. But the big decrease in federal employment (all of it outside the Defense Department) is the result of lower personnel ceilings and/or budget cuts ordered by Congress or the White House. That was largely accomplished through attrition.

The total number of federal workers has dropped about 45,000 nationwide (roughly 20,000 of them in this area) since the Reagan administration took over. Nondefense agencies, like Treasury, Health and Human Services, Transportation (mainly because of the 10,000-plus fired air traffic controllers) and Commerce, took the biggest cuts, while civilian employment in Army, Navy and Air Force actually has increased.

Federal employment here goes up and down, depending largely on the nation's economic health, war or peace prospects and number of programs created (or eliminated) by Congress and the White House.

The civil service population grew during the depression years, but really shot up for World War II. The war peak was 1945 when there were 265,384 federal workers here.

Washington's federal population was down to 207,400 by 1948, then started a Cold War period buildup, hitting 260,000 in 1952 because of the Korean War.

Federal employment here went down 22,000 jobs during the Eisenhower years. Employment boomed with the advent of the New Frontier and Great Society emphasis on space and antipoverty programs and the Vietnam buildup.

When President Kennedy took office in 1961, there were 238,600 federal workers in Washington.

By the end of the Johnson administration, the federal employe population here had grown to 317,000.

The number of government employes dropped slightly at the start of the Nixon administration, but then began a steady rise (317,000 in 1969) to 333,200 when he resigned in August 1974.

The U.S. worker headcount here under President Ford was 350,000.

During the Carter administration, the number of federal employes here went from 350,000 to 365,200 by 1980.

All of the figures represent the "average" number of federal employes on the payroll here during a 12-month period. The actual number can vary month to month because employment totals generally rise during the summer and drop off other times.

Included in the 2.8 million federal workers are full-timers (2.5 million), the U.S. Postal Service's 663,000 and the Legislative Branch (Congress, Government Printing Office, Library of Congress) and the Judicial Branch.

The Legislative Branch had 38,890 employes in March. That makes it the largest single employer here, followed by Navy and the Department of Health and Human Services.