Because participants in the nation's largest "company" health plan, the Federal Employee Health Benefits Program, are using it less and paying a bigger share of their medical bills, the giant health program now has a reserve of $1.9 billion, federal administrators report.

That is a substantial cushion for a program that will take in $7 billion in premiums this year, and it could mean that premiums will go up only slightly next year or, in some cases, be cut.

Congress requires that a reserve adequate to cover benefits be maintained and that the reserve also be used to hold down premiums. Depending on the plan chosen, those premiums range from a few hundred dollars to as much as $1,300 a year.

The Office of Personnel Management runs the health program, which covers 10 million U.S. workers, family members and retirees around the world, including about half the residents of this area.

Congressional experts say there is a very good chance OPM will use some of the reserves to make premiums more attractive to employes. In January the average premium went up 4 percent, but many plans actual cut premiums.

The government pays about 61 percent of the total premium, according to the OPM.

The federal program now has 210 plans, ranging from giants such as Blue Cross-Blue Shield and Aetna to tiny community-oriented health maintenance organizations. Most workers and retirees in the Washington area are eligible to participate in about 21 of the plans.

One reason for the decline in usage of the program, insurance experts say, is that more and more workers in government and industry are switching to plans that charge lower premiums, but that require the insured to pay higher deductibles and to make copayments for health care.

Fixed fees (maximums that companies will pay for services) are also standard features of more plans, and that has cut into costs and usage.

Whatever the reason for the growth in the financial reserves of the health program, it could mean lower premiums next year for many people. The next health insurance open season will be scheduled for a period in November and December.