The government may decide as early as next week how much time employes must serve in January before they can retire and reap a Medicare-eligibility windfall.

Workers who leave Uncle Sam during Janaury, even if they never have paid into Social Security, will be able to get Medicare coverage for themselves by paying only a tiny portion of the Medicare tax that most Americans pay all year, every year, of their working careers.

Health and Human Services is in the process of deciding how much service time employes must have in order to get the Medicare benefit.

Beginning next year, federal and postal employes will have to kick in 1.3 percent of salary (on amounts up to $32,000) to help finance the Medicare portion of Social Security. They will not have to pay the other portion of the Social Security tax from their federal salary.

In return, employes will be able to count federal service toward eligibility for the Medicare benefit and be covered by Medicare at age 65.

For several thousands of lucky feds who retire in January, the Medicare tax bite will be minimal, yet the benefits will be the same as those for people who have worked all their lives under Social Security.

In approving the Medicare tax for government workers, Congress said that employes who work for only a short period of time during the January transition month will be entitled to full Medicare coverage.

The meaning of the phrase "short period of time" is now in the hands of lawyers and technicians at the Health Care Financing Administration, a part of HHS.

Aware of the Medicare bonanza, thousands of federal workers who originally intended to retire this year are holding off until January. Many have informed their personnel offices that they will stay on only as long as it takes to qualify for Medicare.

They should find out how long that will be -- an hour, a day or as "much" as a full two-week pay period -- probably sometime next week.