While Congress and the White House put the screws to the federal work force, the semi-independent U.S. Postal Service is quietly moving to distance itself, and its workers, from the rest of the beleaguered government establishment. Examples:

* USPS is studying the feasibility of having its own health insurance plan to cover its 600,000 workers and their families. Postal workers now are part of the Federal Employee Health Benefits Program. This covers 9.2 million U.S. retirees, workers and dependents, including about half the population of metropolitan Washington.

Postal officials think they might be able to negotiate a better insurance deal for their employes.

In the past two years, federal workers' health premiums have gone up more than 50 percent while benefits have been cut 16 percent. Postal workers, thanks to their unions, already pay a smaller portion of health insurance premiums than their colleagues in other agencies.

If new postal and federal employes are put under Social Security, USPS will consider setting up its own retirement plan to supplement Social Security benefits.

In a Jan. 17 meeting with a group of postmasters, William Bolger, the postmaster general, noted that unlike other federal agencies, USPS is "free to decide . . . what benefits are necessary in order to attract and retain the kind of quality work force we now have."

Bolger said that any retirement plan USPS sets up would have to be "fully funded by employer and employe contributions . . . and would have to start off actuarily sound and remain that way."

* USPS has advised the unions, which represent 90 percent of its work force, that it does not consider itself covered by legislation that Congress approved last year relating to military retirees who now hold civilian federal jobs. The law said that the civilian salaries of those persons are to be reduced on a dollar-for-dollar basis each time they get a cost of living increase in their military retired pay.

But USPS has advised unions that "the postal service will . . . make no offsetting salary reduction for any military retiree cost-of-living-increases received by postal employees.