For the next five weeks, government employees and retirees will have the opportunity to sort through an array of health insurance plans and select coverage for 2005.

Opportunity, however, does not mean that most employees and retirees will switch plans. Only 4 to 6 percent of enrollees drop their existing coverage and sign up for a different plan, according to recent trend data.

Still, there should be plenty of window shopping, in part because premiums vary widely among plans for next year and because the Bush administration is aggressively promoting "health savings accounts" as a way for enrollees to gain a tax advantage and take control of their health care spending.

Premiums in the 2005 Federal Employees Health Benefits Program will rise an average 7.9 percent next year, less than the double-digit increases of the past four years. As in past years, prescription drug costs are a big driver, accounting for 33 percent of the premium increase.

The FEHBP is the largest health care program in the nation, providing insurance to more than 8 million civil service and postal employees, retirees and family members.

As the 400,000-member National Association of Retired Federal Employees points out in its magazine this month, there is no good way to say which FEHBP plan is best. The plans, NARFE notes, all cover essential services -- such as hospital and doctor care, prescriptions, outpatient lab tests, treatment of mental illness, routine mammograms for women 35 and older and routine prostate cancer tests for men 40 and older.

For the open season that begins tomorrow and ends Dec. 13, the FEHBP will offer 249 options, with the large majority of them health maintenance organizations available only in certain geographic areas. Enrollees in the Washington area will be able to choose among 21 plans, including HMOs and fee-for-service plans.

Blue Cross and Blue Shield is the most popular choice: 54 percent of government employees and retirees are enrolled in the standard and basic options. Other popular plans include the Mail Handlers Benefit Plan and the Government Employees Hospital Association.

While health care analysts caution against judging health plans based on price, variations in premium increases for those three popular nationwide plans underscore why it is important to read carefully your health plan's brochure for 2005 and determine how much your premium costs are changing.

The employee share of premiums for Blue Cross and Blue Shield's standard option is rising by 3.7 percent for individuals and 4.6 percent for families. The cost to enrollees in GEHA's standard-option coverage is increasing about 10 percent for individual and family coverage. The Mail Handlers standard option is jumping 40 percent for individuals and 37 percent for families.

According to FEHBP charts, some of the popular HMOs in the Washington area, such as Aetna, Kaiser Permanente and M.D. IPA, are raising premiums by less than 10 percent.

And not all plans are raising their prices. CareFirst BlueCross BlueShield, for instance, is cutting its HMO premiums.

For 2005, the Office of Personnel Management, which administers the FEHBP, has added 18 high-deductible insurance plans that offer health savings accounts, or HSAs. With an HSA, an enrollee makes a tax-deductible contribution to a savings account. The account is used for routine medical costs, tax free, and the high-deductible plan covers serious illness or injury.

HSAs are available to people who are not enrolled in Medicare and do not have other insurance. Since the rules typically exclude retirees, OPM is offering them a similar account, a "health reimbursement arrangement."

Although OPM is talking up HSAs and HRAs as a way for families to take control of their health care spending and save for the future, officials said they have no estimates of how many FEHBP enrollees may switch to high-deductible plans.

More than 13,000 people have signed up to receive information about HSAs by e-mail from OPM, a spokesman said. Officials have noted that a similar product -- the "consumer-driven option" -- was introduced into the FEHBP in 2002 and has only about 16,000 enrollees.