When Ronald Reagan came to Washington in 1981, 13 of every 100 federal employees worked here; when he leaves next year, it will be about 11 out of 100.

While federal employment under President Reagan has grown by 3 percent, to slightly more than 3 million, it has occurred in military bases and post offices around the country, meaning that most domestic agency cutbacks have hit here.

Federal employment is higher in California than in the District of Columbia, higher in New York than in Virginia, and higher in Pennsylvania than in Maryland.

Outside the capital, Reagan's buildup has been spread remarkably evenly, in part because it occurred primarily in the Defense Department, the Veterans Administration and the Postal Service.

Florida is the state that has gained most: Federal employment jumped 23 percent from 1980 to 1986 -- hand-in-hand with the state's population.

More than 15,000 of the 19,000 new employees work for the Postal Service. A spokesman for Sen. Lawton Chiles (D-Fla.) said that the state's population has grown so fast that last year the Postal Service had to pepper the state with new zip codes.

Tennessee was the biggest loser, down 13,280 jobs, about an 18 percent drop. Almost all of the losses followed the closings and abandoning of the Tennessee Valley Authority's 17 nuclear power plants in the early 1980s, according to a spokesman for Sen. James R. Sasser (D-Tenn.). TVA's $14 billion nuclear fiasco prematurely idled thousands of construction workers who were on the federal payroll.

The TVA disaster spilled into other states, including Mississippi, which lost 13 percent of its federal jobs in the Reagan era.

Other big losers are aberrations. For example, Idaho, which is two-thirds owned by the Bureau of Land Management and the U.S. Forest Service, had extensive forest fires in 1980 and staffed up with temporary workers to handle them. The forest fire season in 1986 was less severe.

Texas gained 16 percent more federal jobs, virtually all of them in the Postal Service, the Army and the Air Force.

Meanwhile, in the Washington area, 15,799 federal jobs were cut between 1980 and last September, according to congressional statistics.

Total federal employment in the metropolitan area was 350,001 as of last September.

But the number masks a more significant trend: the use of contractors to perform government work.

An internal Pentagon memorandum estimates that 3 million people are working under contract to the Defense Department. Some, but by no means most, are clustered around the Beltway.

The National Journal estimated in 1979 that for every worker on the federal payroll, four were working indirectly for the national government.

These "indirect" employees include contractors who train federal workers, janitors who clean federal buildings and the research and development groups, popularly known as "Beltway Bandits."

The role of the federal government in the local economy has shifted dramatically in recent years, said Philip M. Dearborn, vice president of the Greater Washington Research Center. Although the federal government remains the area's largest single employer, direct employment has declined while federal purchases of goods and services have risen steadily.

The geographical distribution of federal jobs was once highly controversial as each area of the country sought a greater share of federal spending, but those disputes have died down.

Pentagon employment, however, has remained under intense scrutiny because it is one of the few sources of new federal funds under Reagan.

Civilians perform about one-third of the Defense Department's jobs -- half of the research and development work, and about 95 percent of the employment at depots, shipyards and other logistics centers.

Pentagon figures show that logistical bases, shipyards and research and development facilities have grown, while many other bases have stayed roughly even, or have lost civilian jobs. In this fiscal year, however, cutbacks in military spending have focused on the logistics bases, which employ the most civilians.

In the meantime, a huge Postal Service employment buildup started in 1984 has leveled off in the last few months of 1987. The Postal Service says it hired full-time workers to avoid excessive overtime costs in areas where population growth and an increase in the volume of mail require it. ----------------------------------------------------------------------

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-----CHANGES IN NUMBERS OF FEDERAL EMPLOYEES IN SELECTED AREAS---- ----------------------------------------------------------------------- STATE-------------------- 1980 ------- 1986 ---------

----------------- ADJUSTED --- ADJUSTED--% CHANGE Alaska..................15,571.......14,459......-7% Connecticut.............20,147 ......23,347......+16 Delaware.................4,809........5,385......+12 District of Columbia...230,634......208,458......-10 Florida.................83,052......102,249......+23 Georgia.................77,337.......86,849......+12 Idaho...................11,293........9,797......-13 Maryland...............134,153......130,683.......-3 Mississippi.............28,341.......24,629......-13 Montana.................12,877.......11,106......-14 New Hampshire............6,667........7,413......+11 New Mexico..............27,754.......25,882.......-7 North Carolina..........42,126.......45,706 ......+9 North Dakota.............8,759........7,801......-11 Rhode Island.............9,116.......10,183......+12 South Dakota............10,225........9,204......-10 Tennessee...............71,906.......58,626......-18 Texas..................149,930......174,501......+16 Virginia...............145,278......157,576.......+8 Wyoming..................6,838........6,374.......-7 U.S. Territories........14,218.......17,420......+23 Foreign ...............110,295 ....129,284 ......+17