Yes, under Public Law 97-253, you can have your military service time after 1956 count toward your Civil Service Retirement. However, individuals that first became subject to Civil Service Retirement System deductions after Oct. 1, 1982, must make a deposit to receive credit for their military service in their CSRS or FERS annuity. CSRS covered employees prior to Oct. 1, 1982, may choose not to make the deposit and still receive credit toward the annuity, but would, if they are eligible for Social Security benefits, would at that time lose credit for military service in their CSRS annuities and their annuities will be reduced. If you pay the deposit, you will receive credit for their military service under CSRS and Social Security.
Source: federal-newsgroup.blogspot.com
Go to OPM for more info