The estimated 400,000 federal and District government workers in the Washington area could save $300 or more in health insurance costs next year if they take the time to pick an insurance plan that best suits their needs, a new consumer's study showed yesterday.

The survey of the 30 health insurance plans available to federal and D.C. workers in Maryland, Virginia and the city shows that while the benefits from several plans may be virtually identical the premium and health care costs are often substantially different.

Moreover, the study by the Washington Consumers' Checkbook magazine showed that some high-cost plans do not provide the range of health care options that less costly plans do.

The survey showed that the most popular insurance plan, the Blue Cross-Blue Shiled high option plan, is consistently, one of the most costly. cNonetheless almost half of the government workers here have signed up for that plan, the magazine stated.

Conversely, Robert Krughoff, Checkbook's publisher, said that relatively few workers have chosen the Government Employees Hospital Association (GEHA) insurance plan, despite the fact that its costs are often much cheaper than virtually any other plan, regardless of family size, and its benefits often the same or superior.

Krughoff described the GEHA program as "obviously a superb plan."

The survey also showed that Health Maintenance Organization plans, under which consumers typically pay for their health care on an annual fixed costs basis, can also be expensive.

"A big rationale for them is that they prevent unnecessary medical care," Krughoff, said. With a fixed payment schedule, "They eliminate the incentive for doctors to prescribe more medicine and surgery."

But the survey showed that such preventive care health plans are among the most costly here, because the premiums often are so high that they more than outstrip the savings in the out-of-pocket expenses that traditional health plans require.

The survey urges individual government workers to study thoroughly the various plans and their own personal medical care needs before finally selecting one. This was particularly important, the magazine said, if an individual of family is expecting unusual expenses, such as bills for dental or psychiatric care, that one plan might cover and another with the same premium might not.

Such insurance choices are relevant at the moment for federal and D.C. government workers, the magazine said, because the workers have their annual opportunity to switch insurance plans between next Monday and Dec. 7.

The magazine said that the vast differences between plans could easily be illustrated by comparing their highly ranked GEHA plan for a family of four with the lowly ranked Blue Cross-Blue Shield high option plan.

The study showed that in an average year the GEHA plan would cost about $680, including $235 in premiums and about $445 in unreimbursed expenses. The Blue Cross plan for about the same coverage will cost $1,040 in an average year, about $360 more than the GEHA plan.

While the Blue Cross plan would reimburse a greater proportion of a patient's bills, the premiums will be more than $450 higher.

"Over a 20-year period you will probably save over $5,000 by selecting GEHA," the magazine said. 'Of course everyone would not have this much, and some families would actually come out ahead under the Blue Cross high option plan. But other families, the luckiest ones, would come out even more than $5,000 ahead under GEHA."

Washington Consumers' Checkbook is published by the nonprofit Washington Center for the Study of Services, a group that previously has produced surveys of a variety of often-used consumer services.