Federal workers who pay an average of about $800 a year for health insurance coverage may be hit with a 1983 premium increase of between 20 and 25 percent.

Insiders predict that next year's premium jump for the 9 million workers, family members and retirees in the Federal Employee Health Benefits (FEHB) program will not be accompanied by a drop in benefits. This year health insurance premiums went up an average of 20 percent, while most plans cut back benefits anywhere from 12 percent to 16 percent.

Details of the 1983 FEHB -- rates charged and benefits offered by the 100-plus plans in the program -- will be officially announced within the next few weeks. There will be an open season enrollment period before the end of the year for workers and retirees who want to switch plans for the 1983 year.

Contract negotiations between the government and carriers in the FEHB are handled by the Office of Personnel Management. OPM Director Donald Devine is scheduled to testify tomorrow before the House Compensation and Employee Benefits subcommittee (of the Post Office-Civil Service Committee) chaired by Rep. Mary Rose Oakar (D-Ohio).

Employes this year will pay nearly $2 billion in premiums into the FEHB. The government will contribute almost $3 billion.

Uncle Sam is supposed to pay 60 percent of the premium -- based on a complicated formula dealing with the average premium of the six largest carriers in the program. The result is that the amount of premium paid by the government varies depending on which plan workers choose.

OPM, as reported here in April, is considering a voucher system whereby the government would give employes a flat payment (with a slightly higher payment for retirees) to use to pay all, or part, of their health tab -- depending on the price of the plan they chose. Congress would probably have to approve such a change.

Meantime, program watchers expect a premium rise next year. They do not, however, believe that plans will cut benefit levels, though some are expected to shuffle some benefits, raising coverage in some areas and lowering them in others.