A week from tomorrow, more than 4 million federal workers and civil service retirees will begin their annual health insurance hunt.

The task is never easy. This year -- because of an average premium increase of 31 percent -- picking a health plan will be tougher than ever. The plan you pick during the Nov. 9 through Dec. 11 open season will be the one for which you pay premiums through 1988. It will be the plan that will cover your medical, dental and hospital bills next year. The right choice could save you more than $1,000.

More than half the people in the Washington area are covered by the federal health insurance program. Nationwide, it covers 12 million civil servants, postal employes, family members and retirees, and in some cases the ex-spouses of federal employes.

The rankings below were worked up by Government Retirement Benefits Inc., an Alexandria-based firm that shortly will publish a special health insurance guide for U.S. workers and retirees. Its detailed rankings tell the best plans for singles, families, retirees, persons with special health problems and those looking for maximum dental benefits. Rankings shown today from GRB are based on three primary considerations: catastrophic insurance protection, customer satisfaction and the cost to you (premiums and out-of-pocket expenses) for an average year of medical costs.

Bear in mind the rankings do not list any health maintenance organizations. GRB officials said there are just too many of them. But later listings will rate HMOs that offer some of the best benefits at the lowest cost.

Today's GRB ratings are limited to plans open to all workers and retirees. Ratings for other plans will come later:

For single, nonpostal workers, GRB gives the nod to: National Federation of Federal Employees standard option; National Association of Government Employees standard option; National Treasury Employees Union; National Alliance of Postal and Federal Employees standard option; Aetna standard option; American Postal Workers Union; GEHA plan; National Association of Letter Carriers; American Federation of Government Employees standard option; Blue Cross-Blue Shield standard option; Postal Supervisors; NAGE high option; NFFE high option; Mail Handlers high and standard options; Postmaster standard option; AFGE high option; Alliance high option; Aetna high option; Blue Cross-Blue Shield high option, and Postmaster high option.

For a nonpostal family of three, GRB ratings suggest: National Federation of Federal Employees standard; National Treasury Employees Union; American Postal Workers Union; GEHA plan; Blue Cross-Blue Shield standard; National Association of Letter Carriers; National Alliance of Postal and Federal Employees standard plan; National Association of Government Employees standard plan; American Federation of Government Employees standard; Mail Handlers high and standard options; Postmasters standard option; Aetna standard option; Postal Supervisors; AFGE high option; NAGE high option; NFFE high option; Aetna high option; Blue Cross-Blue Shield high option; Alliance high option and Postmasters high option.

GRB's 100-page guide is available at 5400 Eisenhower Ave., Alexandria, Va. 22304, or by calling 461-9100. Single copies cost $5.95, plus $1.75 postage.