Health insurance premiums that many federal workers and retirees consider too high already will be going up again next year.

The new premiums and benefits of the 400-plus plans in the program will be announced next month. Insurance shoppers will have an open season -- from Nov. 13 through Dec. 10 -- when they can pick their 1991 plans.

Under the federal health program, young workers and retirees in the same plan pay the same premiums, and get the same benefits, regardless of their age and health. Many retirees resent paying premiums for coverage of things such as maternity benefits they no longer need.

Many younger workers feel they are paying higher premiums to subsidize retirees who tend to have higher medical bills.

A number of people have argued that there should be one policy (and premium) for workers and another for retirees. This, they say, would make for a better system since one age group wouldn't feel it was subsidizing another age group.

On July 23, we ran a letter from a federal retiree who didn't buy the argument that older workers and retirees are the heavy users.

He said most have Medicare, which offsets many of their costs. Many retirees have complained that they must buy "family" coverage for two people, paying the same premium as a young couple with six children.

The subsidy issue has brought a response from Harry P. Cain II. He is senior vice president of Blue Cross-Blue Shield, the largest plan in the federal health program. This is what Cain says about the issue of subsidies and risk-sharing:

"Based on our experience in the federal program (and it is not very different from health insurance experience elsewhere) the average annual health care expenditures under the federal program are about as follows, using 1988 data:

"Employees under age 30 single, $500 a year and family, $1,750 a year. Age 30-50, single, $850 and family, $2,050. Age 50 to 65, single, $1,500 and family, $2,850 per year.

"Retirees (all ages), single without Medicare, $2,550 per year and $3,990 per year for a family without Medicare. For retirees with Medicare the single annual average expenditure is $1,200 and the family is $2,500.

"As your readers will see health care expenditures . . . on average escalate with age. The issue in most need of response is 'who is subsidizing whom?' No matter what the age group, the fact is that a very small number of people (5 percent) use a majority (50 percent) of health care services and resources. The vast majority of us (80 percent) together cause only 20 percent of the total expenditures. But that is what makes insurance possible.

"The concept of insurance is to spread the risk of the comparatively few expensive illnesses over all potential users.

"In other words, the purpose of insurance is to have the large majority 'subsidize' the small minority.

"No subsidies, no insurance."