Federal health insurance hunters looking for the best dental coverage have their homework cut out for them during this open season.

Between now and Dec. 7 the 500,000 U.S. workers and retirees in the Washington-Baltimore area must select the health insurance plan they wish to cover them -- and their families -- in 1985. One of the toughest parts of that search is finding a plan with good dental benefits.

The federal employe health program helps pay medical bills for nearly half the people here. Nationwide it covers 10 million feds, family members and retirees. The "best" health insurance plan for you depends on a number of things: your age, health, family situation and how much you can afford to pay for premiums next year.

Health insurance hunters face a bewildering array of plans -- and options within plans -- to chose from. Premiums next year will range from $300 to $1,600 depending on the plan chosen. There are about 140 plans in the program. Washington area feds are eligible to select from about 20 of those plans.

Last Monday we listed the best overall insurance buys as rated by Washington Consumers Checkbook magazine. Those ratings assumed a federal family of four and listed total costs -- including premiums and out-of-pocket charges -- for families who anticipate "average" medical expenses in 1985.

In later columns will be listed Checkbook's recommendations for retirees and for persons anticipating heavy medical costs next year. The full Checkbook guide goes on sale tomorrow at area newsstands.

Today we will take a look at dental insurance coverage. If dental coverage is important to you, be advised that some plans are much better than others.

Best overall coverage, according to Checkbook, is provided by two local health maintenance organizations: The George Washington University plan and the MD-IPA plan. They have no deductible and no maximum benefit, and they cover preventive care and most costs for common procedures.

Many of the national plans cover about half of all dental costs. These include both Aetna's high and standard options; Government Employees Benefit Association; Mail Handlers high option; NAPUS; National Federation of Federal Employees plan; National Treasury Employees Union standard option; Postmasters high option and the Rural Letter Carriers plan. Before you select any plan, read its brochure carefully to determine what it covers for dental procedures you may need.

Checkbook also recommends that employes and retirees consider dental benefits offered by the American Federation of Government Employees standard plan; Blue Cross standard plan; National Association of Government Employees; Letter Carriers; NTEU, Postal Supervisors and Special Agents Mutual Benefit Association plan.

Persons interested in the best orthodontic coverage -- at least half the total cost -- should consider the following plans: Foreign Service; GWU; MD-IPA; NTEU and the Postmasters high option. Waiting periods and maximum reimbursements vary from plan to plan. So check the brochures carefully. Also, many of the plans that offer the best orthodontic coverage are among the most costly, so consider whether the extra premium is worth it.

Checkbook advises that even if you do not anticipate heavy dental bills, the plans offering the best dental coverage (even if they cost more) could save you money. For example if a family of four runs up a 1985 dental bill of $400, many of the plans listed above would cover at least half of that cost.

Also, when checking health plan brochures (available at federal agency health insurance offices and from the plans themselves) be aware that not all of them are written in basic English. Many use the term "gingival" (that is your "gums"), or use "aleveolar" when they mean "jawbone" procedures. Good hunting!