Federal and postal workers accustomed to annual increases in health premiums -- and corresponding cuts in benefit coverage -- may get some moderately good news this fall.

Although the government has not announced what 1986 premiums will be, indications are that most of them will be modest and that some of the larger plans may actually cut 1986 premiums. That would be a big help to feds who face a pay freeze next year.

In the past, increases in premiums were largely offset by pay raises. Last January, for example, premiums went up an average of 4 percent, according to the Office of Personnel Management (although some plans had much larger raises and some actually cut premiums), but at the same time workers got 3 1/2 percent pay raises.

But because pay was frozen at current levels in the 1986 budget approved by Congress, even a modest premium increase next year could mean a cut in take-home pay for many workers.

One of the legacies left by former OPM director Donald J. Devine, who once worked in the insurance industry, is a health system that requires individuals to pay bigger deductibles and/or more of the cost of health care out of their own pockets. The changes in the federal system mirror a trend in the private sector.

Because of bigger deductibles and rules that increased the policyholders' share of payment, there has been a decline in the use of health insurance by federal workers and private industry employes. That in turn created surpluses in many health plans, which base their premiums on anticipated usage and costs over a 12-month period.

Blue Cross-Blue Shield has proposed rebates to current federal and postal worker subscribers and to retirees.

Other plans in the program have rejected the rebate idea and instead may hold the line or cut the cost of premiums next year.