What promises to be one of the world's biggest, most confused hunting seasons opens Monday for 9.2 million U.S. workers and families who are counting on the federal health program to pay part of their dental, mental, health and hospital bills next year. The enrollment/change period will run at least two weeks, and require government workers to make some major financial decisions with minimum information available.

The open season comes after months of legal battles between health plans (anxious to keep certain benefits) and the Office of Personnel Management (anxious to cut benefits and costs). OPM was rebuffed in its attempts to eliminate abortion benefits, and cut many benefits (and premiums) next year. But the legal fighting ate up a lot of time and so confused the insurance picture that OPM tried to postpone "indefinitely" the open season that was due to begin in early November.

The U.S. personnel agency said it would take 8 to 10 weeks to print and distribute brochures -- showing benefit and premium changes in the 126 plans in the program -- once those benefits and premiums finally were settled. In effect OPM said it might have to lock everybody in his or health plan for another year, no matter what changes plans made in premiums (some plans will raise rates from 5 percent to nearly 50 percent) or in benefits. But U.S. District Court told OPM to start the open season on Dec. 7, and that has been upheld on appeal. So the open season is on.

This year's "brochures" will be in the form of a giant (60-90 page) press release OPM will issue Friday outlining prices and benefit changes. Copies will be sent to agencies. It will be up to them to make either individual copies available to each person, or reading copies available in agency libraries or personnel offices.

Because of the complexity of outlining new premiums and benefits -- some plans still are not settled --OPM says that agencies can, on their own, extend the open season beyond the two-week period ordered by the judge. Unless the U.S. Court of Appeals this week blocks the open season (when employes can change plans or coverage for 1982) it will begin Monday. And it will run for at least two weeks, maybe longer in some agencies.