Workers and retirees hit with heavy medical bills in 1991 can expect to pay anywhere from a few hundred dollars to almost $10,000 out of their own pockets, according to health insurance expert Gordon F. Brown.

What you may have to pay next year will depend on which health plan you pick during the open enrollment period that starts Nov. 13 for people in the Federal Employee Health Benefits Program.

The program covers more than 11 million people, from members of Congress and CIA agents to government lawyers, postal clerks, D.C.'s mayor and the spouses or survivors of U.S. employees and retirees. About half the people in the Washington area are covered by the program.

Brown ran the federal health program until his retirement. He says all the plans are good. But some, depending on your age, health, family status and income, are better than others, as he points out in his "Open Season Guide" book. It goes on sale today ($10 plus postage); write Employee Benefits Review, 715 Eighth St. NE, Washington, D.C., 20003, or call 202-546-3394.

Insurance experts say the most important feature of any health plan is how well it covers costs associated with catastrophic illness. Brown says many health maintenance organizations provide excellent coverage at low premiums and with minimal out-of-pocket costs to workers and retirees. HMOs stress comprehensive care and preventive medicine better than traditional fee-for-service plans. HMOs also cover things such as physicals, shots and vision and hearing tests that aren't provided for in fee-for-service plans.

But many people don't like the HMO concept. "Generally, when you enroll in an HMO you give up control over your own medical care," Brown said. "The HMO's physicians decide how much, and the kind of, medical care you should receive and when you should receive it."

Here are Brown's ratings for maximum out-of-pocket costs for a family of three next year. They include the total premium cost, membership fees and fees that you must pay before the catastrophic protection benefit limit is reached. These ratings don't apply to persons with Medicare Part A and B or only Part B because they have better catastrophic coverage.

The three-person family with the Government Employees Hospital Association plan could expect to pay a maximum of $3,076 out-of-pocket next year.

The same family with the American Postal Workers Union plan would pay $3,173, Brown said. The family would pay $3,855 with the National Treasury Employees Union plan; $3,915 with Blue Cross-Blue Shield's standard option; $4,154 with the Postmaster standard option plan; $4,564 with the Alliance standard option plan; $5,119 with the National Association of Letter Carriers plan; $6,904 with the Mail Handlers high option plan; $7,017 with the Postmaster high option; $7,098 with the Blue Cross-Blue Shield high option plan; $7,755 with the Mail Handlers standard option and $9,491 with the Alliance health plan.