Health insurance refund checks for 2 million federal employes and retirees, including nearly 350,000 in the Washington-Baltimore area, will be mailed early next month.

About a dozen insurance plans participating in the federal health program are offering the refunds to 1985 policyholders. Amounts will depend on the plan and the coverage participants signed up for last year.

The refunds in the federal program are the result of a big buildup last year in financial reserves. The insurance plans said that participants used their coverage less and paid a larger share of their own medical bills. The government, which pays about 61 percent of the average employe's health premium, will get more than $750 million in refunds from the insurance companies.

The long-delayed refunds were approved when President Reagan signed a bill last week allowing retirees, who had been excluded from the rebates, to get the same amounts as active-duty workers.

Blue Cross-Blue Shield says letters will be sent to 1.4 million people in mid-March. Recipients will be asked to confirm amounts due them and their current addresses. The company said checks will be mailed around April 1. Other health plans are expected to follow a similar timetable.

Other plans offering refunds are Aetna, National Association of Letter Carriers, Foreign Service plan, American Federation of Government Employees, Government Employees Hospital Association and the Government Employees Benefit Association.

Some of the plans still haven't worked out refund details. Here's a rundown of those that have and what the refunds will be. Postal workers will generally get smaller amounts because the government pays a bigger share of their premiums:

*Blue Cross-Blue Shield: The high-option refund will be $354 for family plans and $164 for single coverage. Standard option refunds are $169, family and $69 for single coverage. Postal refunds are $284 for family high option; $133 for single high option; $48 for standard family coverage and $17 for single coverage.

*Government Employees Hospital Association: Nonpostal refunds are $76.80 for family coverage and $42.54 for single coverage. Postal refunds will be $19.59 for family coverage and $16.97 for single coverage.

*National Association of Letter Carriers: For nonpostal employes the family option refund is $61.52, and $35.91 for single coverage. For postal workers the refunds will be $36.82 for family coverage and $24.84 for single coverage.

*American Federation of Government Employees: High-option family refund is $47.96 and the single-option refund is $23.19.