Federal employes who credit their post-1956 military service toward civil service retirement can avoid having their annuity reduced when they become eligible for Social Security at age 62 by paying the government the equivalent of 7 percent of their military earnings received after Jan. 1, 1957.

Military payroll offices are backlogged with requests from U.S. workers and retirees who are trying to figure out their post-1965 military earnings so they will know how much they must put into the CS fund to avoid the annuity reduction.

Many veterans say they are having a hard time getting earning statements from their former services. The exception is the Navy, which a number of callers say has been supplying the important data promptly.

To get the information on earnings, write the finance office of the military branch in which you served:

Army: Commander, Finance and Accounting Center, Dept. 88, Indianapolis, Ind., 46249.

Navy: Commanding Officer Finance Center, Attn: 43C, Celebreeze Federal Building, Cleveland, Ohio, 44199.

Air Force: Commander, Accounting and Finance Center/ASC, Denver, Colo., 80279.

Coast Guard: Commanding Officer, Settlement and Records, Retired Pay Center, 444 South East Quincy St., Topeka, Kan., 66683.

Public Health Service: Director, Commission Personnel Ops Division, PHS, Parklawn Building, Room 4-35, 5600 Fishers La., Rockville, Md., 20857.

National Oceanic and Atmospheric Adm.: Department of Commerce, NOAA, Rockville, Md., 20852.