Federal workers and retirees who are expecting health premium refunds will probably have to wait until January because the Senate will not give its approval until after the Thanksgiving recess.

A number of federal health plans are offering refunds to more than 2 million current subscribers, including 300,000 federal employes and retirees here. Depending on the plan and coverage, subscribers are due refunds ranging from less than $20 to more than $400.

The refunds are the result of a drop in insurance usage this year, and an increase in the percentage of health bills policyholders are paying.

The unprecedented, multimillion-dollar refunds have already been approved by the Reagan administration, the House and the Senate Governmental Affairs Committee and now await full Senate action.

Once congressional action is completed, insurance companies will inform subscribers about amounts due and will verify addresses. All this will take time.

Most of the 1.4 million people due refunds belong to the Blue Cross-Blue Shield plan. It is proposing to refund $280 million to individuals and about twice that to the government, which pays most of the total premium.

Blue Cross-Blue Shield has also set aside $25 million for possible reimbursement if it loses a class action lawsuit brought by 1983-84 subscribers who also are seeking refunds. If those subscribers lose, the insurer plans to divide the $25 million among 1985 policyholders.

Other plans offering refunds to current subscribers include Aetna, Government Employees Benefit Association, Government Employees Hospital Association, the American Federation of Government Employees, National Association of Letter Carriers and the Foreign Service health plan.

Some of the health plans not offering refunds contend that the rebates are an ill-conceived public relations stunt that could cause premium increases in future. They argue that surpluses from the plans should be plowed back into the program to keep premiums down in coming years.

If you are in a health plan that is offering a refund you will still get it, even if you switch to another insurer during the current open enrollment period.