After a delay of nearly a year, Blue Cross-Blue Shield will mail out 1.4 million forms today notifying federal policyholders about the size of their 1985 premium refunds.

About 300,000 people in the Washington-Baltimore area are owed refunds from the nation's largest health insurer. Checks are expected to range from $69 to $354.

Half a dozen other health insurance plans are also planning to make refunds to federal subscribers.

In early April, after verifying their addresses, Blue Cross-Blue Shield will begin mailing out $270 million in refunds.

Federal workers and retirees have awaited the refunds since last spring, when Blue Cross-Blue Shield proposed them. James N. Gillman, the company's vice president for federal programs, said the refunds were made possible by an "unanticipated drop in the use of hospital and medical services by our subscribers."

The Reagan administration approved the unprecedented refunds last year. But they were delayed after the Justice Department said special legislation would be required to make payments to retirees, who pay the same premiums and get the same coverage.

After several months, Congress approved a retiree refund bill. But President Reagan vetoed it because the House had added unrelated language that he said would raise the government's insurance costs.

Another refund bill, minus the language the White House opposed, cleared Congress early this year, setting the stage for the payout.

The refund amount depends on the kind of coverage the recipients had in 1985. Nonpostal employes and retirees with high-option family coverage will get $354; those with high-option single coverage will get $164. Those with standard family coverage will get $169 and those with standard single coverage will get $69.

Because the U.S. Postal Service pays a bigger share of the premiums for its employes and retirees, refunds for its employes and retirees will amount to $284 for high-option family coverage and $133 for high-option single coverage. Postal workers with standard family coverage will get $48 and those with standard single coverage will get $17.

Other health plans offering refunds to Washington area federal workers include the American Federation of Government Employees; National Association of Letter Carriers; Government Employees Hospital Association; Government Employees Benefit Association, and the Foreign Service health plan.