Premiums charged by some of the major plans in the country's biggest company health program, the Federal Employees Health Benefits Program, may jump from 20 to 40 percent in January because of skyrocketing medical costs and increased usage by the 10 million federal workers, retirees and family members covered by it.

Government employes, who are anticipating a 3 percent salary increase in January now pay from $250 to $1,900 per year for insurance, depending on which of the 400 health plans they pick.

The plans help cover doctor, dental and hospital bills for more than half the people in the Washington area. Premium- payers include retired clerks and ex-presidents, as well as government lawyers, astronauts, CIA agents, members of Congress and their families.

The health plans include giants such as Blue Cross/Blue Shield and Aetna, as well as health maintenance organizations, and special plans offered by unions or limited to law enforcement personnel, foreign service families or staffers at the super-secret National Security Agency. People here can pick from about 20 plans and change coverage during open seasons in November and December.

A few of the smaller plans may cut premiums, as some did this year. But the average premium went up 14 percent. The government pays an average of 60 percent of the total premium for white-collar workers and up to 75 percent for unionized postal employes.

Last year the premiums dropped an average of 6 percent. That was primarily because of decreased usage and because employes (due to earlier cost containment programs) were paying a bigger share of the costs out-of-pocket. The decline was reflected in refunds of more than $300 million that half a dozen plans made to policyholders. They also refunded more than half a billion dollars to Uncle Sam that year.

However, insurance analysts say that recently national medical costs have risen about seven times as fast as the inflation rate. Also, they say, policyholders nationwide are using their insurance more often, and for more lengthy and costly treatments. Insurance trade newsletters have predicted industry premium hikes this year of 15 to 20 percent.

Many private firms are cutting benefits, requiring workers to pay more of the premium, accept higher deductibles and reduced benefits to cut costs. The government position has been to hold the line on benefits that were trimmed substantially in the early 1980s.

Although half a dozen experts in the federal program predicted big increases in many of the major plans, none would say so on the record. Negotiations between the Office of Personnel Management and insurance plans begin next month for 1988 coverage and premiums.

Insurance specialist Gordon Brown, secretary of the 600,000- member National Association of Retired Federal Employees, says he has kept up with insurance trends in industry and that the picture is "grim." Brown was formerly assistant OPM director for insurance programs and says his contacts in the industry are predicting "significant" increases in many federal health plans.

Brown takes issue with insurance plans that blame high costs on heavy concentrations of retiree subscribers. He said many government retirees have Medicare coverage that pays about 45 percent of their bills. Plans with heavy concentrations of federal retirees have indicated privately that they will seek substantial 1988 increases, but they say the higher costs are also the result of an upsurge in usage that is reflected in private health insurance plans.