Lots of calls from government workers with post-1956 military service who want to know about any interest charge on payments they plan to make to the civil service retirement fund.

Here is the official word on interest from the Federal Personnel Manual 831-77, dated March 10:

"No interest is charged if a deposit for military service is made before October 1, 1984, or within two years after the date the individual becomes employed in a position under the civil service retirement system, if later.

"If the deposit is not completed within the grace period, interest is charged at the rate of 3 percent per year from October 19, 1984 (or two years from the date the individual first becomes a covered employe, whichever is later) through December 31, 1984, compounded annually. Periods of separation on or after October 1, 1982, will be used in determining the grace period, regardless of when the period of separation began.

"Effective January 1, 1985, the interest rate charged on deposits for military service will change from 3 percent to a variable rate that will be determined by the Treasury. This determination will be made each calendar year on the basis of the average yield of new investments purchased by the retirement fund in the previous year."

The problem, of course, is that both the Army and Air Force say it may be months before they can supply military pay data to persons who need it, in order to determine how much they must pay into the civilian federal retirement program. If employes can't get the data, they can't make the payments and if they don't make the payments by the deadline, they will be charged interest.