The enrollee share of premiums in the health-care program for federal employees and retirees will increase by 1.5 percent on average in 2019, although there will be decreases in some plans, including in the two Blue Cross and Blue Shield options that account for nearly two-thirds of enrollees, the government announced Wednesday.

Further, Blue Cross and several other plans will offer a new third option in the Federal Employees Health Benefits Program, the largest employer-sponsored health insurance program in the nation, the Office of Personnel Management said.

The FEHBP is open to almost all federal employees, while federal retirees can continue coverage if they were covered for the five years before retiring. It has about 4 million enrollees and about an equal number of covered spouses and children up to age 26.

The large majority of the plans — 265 will be available in 2019 — are health maintenance organizations or fee-for-service plans available only in certain areas. There are 16 nationwide plans, most of them available to all enrollees, although several have limits.

Enrollees in the Washington area will have the choice of 37 plans, officials said.

The government pays about 70 percent of the total premium, except in the case of the U.S. Postal Service, which pays a larger share for its employees, although not for its retirees. The total premium increase will average 1.3 percent, but because of the way the formula works for setting the employer and enrollee shares, the enrollee share on average is increasing by more than the government share.

OPM said numerous factors helped moderate premiums after several years of increases in the enrollee share of about 6 to 7 percent. Those included lower-than-expected claims rates in some plans, renegotiated contracts with health-care providers, expansion of telehealth services, and a long-running emphasis on holding down prescription drug costs, managing chronic conditions and encouraging participation in wellness programs.

Full details of each plan’s benefits and out-of-pocket costs will be released ahead of an open season that will run Nov. 12 through Dec. 10. During that time, federal workers not in the program may join for 2019 — retirees generally can’t newly enroll — and anyone already enrolled can choose a different plan or a different level of coverage.

Although the overall average increase will be the smallest since 1995, Alan Spielman, OPM director of health care and insurance, said in a conference call with reporters: “We want people to not be complacent . . . People should not look at only the premium costs in making their decisions.”

“Low increases are good news, but OPM continues to encourage enrollees to shop for coverage, evaluate alternatives, because even if your plan had a modest increase or a decrease, you still might find a better value by evaluating your needs and the choices that are available throughout the program,” he said.

He added that a “significant number” of two-person enrollments have family coverage rather than self-plus-one, which typically costs less for the same benefits within a plan. In some plans, self-plus-one is slightly more expensive, though, due to the high concentration of retirees with that type of coverage and how the premium formula works.

The non-postal employee rate in the plan with the largest enrollment, Blue Cross Standard, will decrease by $0.93 to $112.23 biweekly for self-only coverage, by $3.74 to $268.21 for family coverage and by $1.27 to $256.54 for self-plus-one coverage. Rates in its basic option will remain flat at $73.72 biweekly for self-only coverage, while decreasing by $3.74 to $177.24 for family coverage and by $1.27 to $170.57 for self-plus-one.

Blue Cross also will offer a new FEP Blue Focus option with biweekly premiums of $53.14, $125.67 and $114.25, respectively for the three types of coverage. That plan will feature preventive care, access to the Blue Cross network of hospitals and doctors, access to generic prescription drugs, and co-pays of $10 each for the first primary and/or specialty care visits.

The new option “is designed for federal workers who are proactive about their healthcare and are effectively managing chronic illnesses for themselves and their families. It includes comprehensive benefits, such as covering preventative services, and is designed to provide individuals with access to affordable care when and where they need it,” William A. Breskin, senior vice president of government programs for the Blue Cross Blue Shield Association, said in an email.

That follows a policy change allowing all participating companies to offer three options of any type. Some already had options involving variants such as high-deductible plans coupled with health savings accounts.

Across all plans, the average non-postal enrollee share will increase by $1.53 to $97.93 biweekly for self-only coverage and by $3.06 to $208.23 for self-plus one. Nearly four-fifths of enrollees are in plans whose premiums will increase by 5 percent or less, OPM said.

The cost for retirees is the same on an annualized basis, although they pay premiums monthly rather than biweekly.

Also in the open season, both employees and retirees may newly enroll or change existing coverage in the separate Federal Employees Dental and Vision Insurance Program. Premiums for FEDVIP dental plans are increasing by an average 1.2 percent, while premiums for vision plans are decreasing 2.8 percent on average. Enrollees in that program get no government contribution.

Starting in 2019, military retirees and their families will be eligible to join the FEDVIP program, and family members of active-duty military personnel will be eligible for the FEDVIP vision plans if they are enrolled in TRICARE, the military health plan.

The open season also allows employees to elect a health-care flexible spending account, a dependent-care account or both. The maximums will remain $2,650 for health-care accounts and $5,000 for dependent-care accounts. FSAs are not available to retirees.

While enrollments in the FEHBP and FEDVIP programs continue automatically for those who make no changes, a new enrollment is required each year for an FSA.