U.S. workers and retirees hoping for a chance to switch to less expensive health insurance this May could be hit with some heavy costs.

It now appears likely that this year they will have to pay two deductibles--the amount of out-of-pocket expenses that must be paid before the insurance kicks in. And there is a possibility that they will have to pay a fee for switching plans and/or give up the right to treatment for pre-existing medical conditions.

Hearings began yesterday (and end today) at the Office of Personnel Management on its proposal to have a May 3-28 open enrollment period when feds could get out of their current insurance plan and move to different coverage beginning in July.

Last November's open season was canceled by OPM although 1982 premiums jumped an average 30 percent. Most plans made government-ordered benefit reductions. Many doubled deductible requirements for their plans.

OPM called the hearings to discuss what requirements, if any, should be imposed if the unusual mid-year open season is held.

Leadoff witness Rep. Frank Wolf (R-Va.) demanded that OPM hold the open season "without strings," that is, without any additional financial cost of benefit penalty to workers.

Wolf, who represents lots of voters who are ticked off by the federal health program, was stern when facing OPM chief Donald J. Devine and three top aides. But he was downright pleasant compared with two Democratic legislators--Steny Hoyer of Maryland and Norman Dicks of Washington. They lambasted Devine and the administration for the confusion in the health program that covers 9.2 million workers, family members and retirees--nearly a million of them in the Washington metropolitan area.

Hoyer, a longtime political foe of the chain-smoking Devine, said the open season should be held as soon as possible. Both he and Dicks said the administration created the problems last year when it tried to cut government outlays for health premiums at the expense of workers.

Devine said he got no takers when he asked some legislators if they would be willing to vote an extra $400 million to pay premiums. Dicks said he didn't ask the right members of Congress.

A spokesman for Blue Cross-Blue Shield said his company--which covers about half the federal work force--supports the May open season. But he didn't look happy, and said changes must be made to protect companies that cover "heavy users" such as retirees, and force carriers that now exclude most retirees to take them as enrollees. He suggested that the government vary its premium contributions according to the age, sex and health of individuals. If OPM doesn't request such legislation, he said, Blue Cross-Blue Shield will.

James J. LaPenta Jr., of the Mail Handlers health plan, said "nothing justifies" delaying the open season. He said the only reason for holding hearings now--rather than last year when open season was canceled--is to protect comprehensive plans with big benefits and big premiums that fear they will lose healthy subscribers during an open season and be left with heavy users.

OPM will decide what, if any, conditions to impose during the open season if there is one.

The prospect of two deductibles in this year and the possibility of transfer fees and other penalties will make it even tougher for workers to decide what to do about health insurance, if they get a chance to switch.