More than 150,000 federal employes-- just over 5 percent of the government's total work force--will be hit with a pay cut next month because of anti-double dipper legislation Congress passed last year to penalize people drawing two checks from Uncle Sam.

The law requires that the civilian federal salaries of military retirees be reduced by the dollar amount of any increase they get in retired military pay over the next three years.

U.S. retirees (civilian and military) got a cost-of-living raise effective the first of this month. The raises for survivor annuitants, disabled retirees and retirees who are 62 or older will be 3.9 percent. Nondisablity retirees under age 62 will get a 3.3 percent COLA.

The raises, which will go to 100,000 retirees in the Washington area, will be reflected in checks they get in early May.

Because military retirees' pensions are going up, their civilian federal salaries will be cut accordingly.

The Defense Department will advise agencies how much of a military pension increase each of their employes is getting. Agencies will translate that increase into an hourly rate and cut employes' civilian salaries by that amount.

This exercise, raising retired pay and cutting salary, will take place this year and again in 1984 (with the next retirees increase) and in 1985. Unless Congress extends the law, the civilian salaries of military retirees will be restored in 1986.

Legislators who wrote the temporary pay-pension offset figured, correctly, that it will save a lot of money. Estimates of the savings run into the millions of dollars. What they didn't figure on, or perhaps care about, was the time and money that will be lost in figuring out how big a raise retirees are getting and then translating that into an hourly pay cut.

Most of the retired military personnel in government (128,009 as of last December) were enlisted men and women, not officers. Many of the officers (retired regulars) are already subject to the dual compensation act, which prevents them from getting full military retirement benefits while they are working as civil servants.

According to a study done by the Office of Personnel Management, the largest number of military retirees are with the U.S. Postal Service, which has 36,454. Next comes the Navy, 27,906, the Army, 27,273, and the Air Force, 22,202. The biggest percentage of military retirees working in a civilian federal agency is with the Marine Corps, where 12.1 percent (2,064) of all employes are military retirees.

Veterans Administration has 8,855 retired military working for it, Department of Transportation 2,914, and GSA 1,836. Agriculture has 1,768, Justice 1,333, Commerce 1,149 and Health and Human Services 1,763.

The OPM study did not include military retirees working for the FBI, National Security Agency, CIA, White House, the House and Senate, Tennessee Valley Authority, or the D.C. Government.

The National Taxpayers Union, which coined the word "double dipper" estimates that there are at least 200,000 military retires working in federal civilian jobs.

All the retirees--except those whose retirement is based on war-related or combat injury or disability--will be taking a pay cut next month to cancel out any increase in retired pay they will be getting.