Federal agencies fired almost as many people during the last 90 days of 1981, when the Reagan economic program began to take hold, than they did during the previous 12 months.

The Office of Personnel Management says that 4,148 civil servants--440 of them in the Washington area--were fired between Oct. 1 and Dec. 31 last year. Data from the Federal Government Service Task Force shows that 4,727 U.S. employes were victims of RIFs (reduction in force) during the 1981 fiscal year from Oct. 1, 1980, one month before President Reagan's election, to Sept. 30, 1981.

Data collected by the OPM (an arm of the White House) and the task force (a bipartisan congressional unit) are often at odds because they use different methods. However, both groups predict further firings are likely in months ahead.

OPM, for example, expects at least 3,366 workers will lose their jobs by the end of March. The task force, headed by Rep. Michael Barnes (D-Md.) says the number of RIF actions could be double the OPM prediction.

The task force counts all nondisciplinary firings -- including those made for reorganization purposes. OPM limits its count to layoffs that are triggered by Reagan economic programs. Whichever version you use, it shows that once fire-proof federal workers are getting burned in near record numbers.

OPM says that during the last 3 months of 1981, 2,996 Health and Human Services employes (mostly in Public Health Service hospitals) were fired but that 1,800 of them were immediately hired by state and local government units.

Labor Department fired 401 people, Agriculture 298, ACTION agency 205 and Consumer Product Safety Commission 90 people during the last three months of 1981. Commerce fired 44, Labor about 400, Transportation 41, Environmental Protection Agency 71 and the Federal Labor Relations Authority 2 people.

Some agencies, facing a 16 percent spending reduction, are asking Congress for some relief. But two major operations, the Office of Personnel Management and General Services Administration, have not asked to be let off the budget hook. Both will have RIFs and furloughs.

Parts of Commerce, Interior,Transportation and HHS plan layoffs and/or furloughs. Treasury is seeking partial exemption from budget cuts.