Refunds due the federal government and many of the 1.4 million U.S. employes and retirees who have Blue Cross-Blue Shield health insurance will be $50 million higher than the $754 million rebate previously announced.

The bigger refund, which will be paid this fall, is the result of a continuing decline in hospital use and medical care costs incurred by subscribers to the nation's largest health insurance company.

Tax-free refund checks due civil servants and retirees currently enrolled in the Blue Cross-Blue Shield health plan will be between 8 and 10 percent higher than was originally proposed by the company. Blue Cross-Blue Shield is the largest plan in the federal health program and the nation's largest "company" health plan. No other health plans have proposed rebates.

More than 10 million federal workers and family members, from Arlington to Antarctica, are enrolled in the federal health program. About half the people in the Washington area -- ranging from senators to switchboard operators -- are covered by the federal program.

Locally, nearly 200,000 federal workers and retirees have Blue Cross-Blue Shield policies. Those with high-option plans will get even bigger refunds than they had anticipated. There will be no increase in refunds earlier promised to persons with standard-option Blue Cross-Blue Shield insurance.

The drop in health plan usage -- part of a national trend as people make fewer visits to doctors and pay more of their medical costs themselves -- means that the total refund will exceed $800 million, it was learned. The government share of the money will be put back into the federal health program.

The White House approved the unprecedented refund proposal several weeks ago. But the Justice Department said that Congress must approve special legislation before retirees can get the rebates.

The Reagan administration supports the legislation. Congress is expected to approve it when it returns next month.

Blue Cross-Blue Shield originally proposed refunds of $374 for nonpostal federal employes and retirees holding high-option family policies, and refunds of $173 for those with high-option single policies. Employes and retirees with standard-option coverage will get $179 and $73 respectively.

Refunds for postal workers and retirees (who pay smaller premiums than regular civil servants) were originally set at $300 for those with high-option family policies and $140 for those with high-option single coverage. Refunds for postal workers with standard coverage were set at $51 for those with family coverage and $18 for those with single policies.

Now, however, those refunds have been increased for federal and postal workers and retirees with high-option coverage.

The new refunds for nonpostal workers and retirees will be slightly more than $400 for those with family coverage and about $190 for those with single coverage. For postal workers and retirees with high-option policies, the refunds will be approximately $326 for those with family plans and just over $150 for those with single policies.

Blue Cross-Blue Shield says that policyholders will be sent applications, which they must sign and return before they can get refunds. Only current policyholders who think the company does not have their proper addresses should call (800) 253-0123 to ask for an application.