The typical white-collar Washington bureaucrat earning $26,000 a year would have to kick in about $13 per biweekly pay period to help finance Medicare under a Reagan administration proposal that may be sent to Congress within the next few weeks.

Federal government workers, who are not now covered by Social Security by virtue of their U.S. jobs, would be required to contribute 1.3 percent of their salary--on earnings of up to $32,400--to help pay for Medicare under the proposal, which is part of a set of recommendations aimed at shoring up the Social Security system.

In return for their contributions to that part of Social Security, all federal employes would become eligible for Medicare coverage. About half of all federal workers eventually become eligible for some form of Social Security benefit, including Medicare, based on Social Security coverage for jobs they had before, during or after they worked for the government.

The Reagan proposal, if Congress buys it, would put all federal workers under Medicare and make everyone pay for it, pumping an additional $300 million to $400 million a year into the fund.

The proposal would not put federal or postal workers under any other form of Social Security coverage (unless they earned it through private sector employment). If approved by Congress, the change would be effective next July.