Strange as it may seem, some of the best plans in the federal employee health benefits program won't accept most federal employees as subscribers during the present insurance-hunting season that ends Dec. 10.

Most workers and retirees are eligible to join any of about 20 traditional fee-for-service plans or local health maintenance organizations.

But most of the best-rated fee-for-service plans are available only to a relatively small number of federal employees, depending on where they work or their job titles. Among the special plans are those available strictly for Panama Canal workers, CIA staff members and members of special organizations representing postmasters or rural letter carriers.

In two rival insurance guides written by experts Gordon Brown ("Open Season Guide" 202-546-3394) and Walton Francis ("Checkbooks' 1991 Health Insurance Plans Guide" 202-347-7283), four of the plans rated among the top five are those limited to congressional employees, Secret Service staff members, Foreign Service officers or certain federal law enforcement personnel.

In previous columns we listed the best buys for regular federal employees. Here's a look at some of the special plans:

Beneficial Association of Capitol Employees. BACE is open to the 37,000 legislative branch employees. That includes people who work in Congress, the General Accounting Office, the Library of Congress or the Government Printing Office. Its single plan has a $150 annual deductible. For a family of three the deductible is $300. Its catastrophic medical coverage limit is $1,500. Once you exceed that limit for the year the plan generally picks up most of the rest of the tab.

By comparison, the Blue Cross standard option, which has similar premiums, has a $2,500 deductible. Next year BACE's annual premium for singles will be $417.72. For families it will be $981.84.

Secret Service Employees Health Association in 1991 will have a $200 deductible and a catastrophic medical limit of $1,000 per person or $2,000 per family, not including deductibles. The single premium will be $415.32. Family coverage will cost $1,038.12.

Foreign Service health plan. It has about 11,000 members and a catastrophic medical limit of $2,000. Next year its single premium will be $485.88. Families will pay $1,454.88 per year.

SAMBA (Special Agents Mutual Benefit Association) is open to employees of the FBI, Drug Enforcement Administration, Bureau of Alcohol, Tobacco and Firearms, Naval Investigative Service, U.S. Marshals Service and the Immigration and Naturalization Service. SAMBA's 1991 single premium will be $479.40, and family coverage will cost $1,609.68. For hospital inpatient service it pays 100 percent of room and board and 90 percent of other costs with no deductible. Its catastrophic medical limit is $1,000 per person or $2,000 for families, not including deductibles.

Francis and Brown rate BACE, the Secret Service, Foreign Service and SAMBA plans among the top five. Unfortunately, most federal workers don't qualify for them.