Single federal workers who are looking for the best health insurance coverage at the lowest cost should consider joining one of the area's health maintenance organizations (HMOs), according to the "best buy" ratings of the Washington Consumer Checkbook magazine.

The health insurance open enrollment period for federal workers and retirees will end Dec. 6.

In earlier columns, we've listed Checkbook's best buys for retirees, for families, for persons looking for the best dental benefits and for those seeking the best protection from extra-heavy medical bills.

Today we will give you Checkbook's ratings for people who are seeking self-only coverage.

First, a word about HMOs. There are two kinds. One is the more traditional prepaid group practice. Persons enrolled in this kind of health plan get their health care from a group of doctors, often in a central facility or hospital.

A new type of HMO is the individual practice association. In this kind of plan, doctors maintain their own private practices but also agree to see patients referred to them by the HMO.

The advantages of an HMO are that it stresses preventive exams and health education, and it saves the patient the trouble of submitting claims. Most services are provided free to plan members.

Checkbook also highly recommends some of the non-HMO health plans that provide excellent, low-cost coverage for singles.

The ratings below list the plans with estimates of what each would cost a single worker, with average medical expenses, next year.

The dollar figures include both premiums and likely out-of-pocket costs:

*Columbia health plan, $490 estimated cost to you next year.

*M.D. IPA (DC), $510.

*Group Health, standard option, $610.

*Foreign Service health plan, $620.

*CapitalCare, $620.

*Government Employees Benefit Association, low option, $630.

*Special Agents Mutual Benefit Association, $630.

*Health Plus, standard option, $630.

*George Washington University health plan, $650.

*Health Plus, high option, $660.

*Blue Cross-Blue Shield, standard option, $690.

*Government Employees Hospital Association, $690.

*Kaiser Mid Atlantic, $700.

*Aetna, standard option, $710.

*Group Health, high option, $710.

*Mail Handlers, high option, $720.

*Choice (DC), $730.

*Network health plan, $730.

*Mail Handlers, standard option, $740.

People who want more detailed information on health plan costs, coverage and complaint rates should get a copy of Checkbook ($4.95) at 347-7283. Health Insurance Help: Federal workers and retirees who are looking for the best health plan for them can get personal advice tomorrow and Monday on the radio.

On Saturday, station WNTR (1050) will have a call-in show from 1 p.m. to 2 p.m., featuring advice from Walton Francis of the Washington Consumer Checkbook magazine. The number for questions is 588-0111.

Monday from 12:30 to 1:30 p.m. station WPFW (89.3) will have a special insurance program called "Buyer Beware, Buyer Be Wise." Listeners may call in at 783-3104 for special consumer information on health plans.