Thousands of people who never worked for the government -- from ex-spouses to adult children -- are still eligible to join the federal employee health program. The open enrollment period ends Monday.

For many, the right to join the U.S. health program is a blessing. It doesn't require physical exams. Nobody can be rejected for preexisting medical conditions, and participants can change plans every 12 months if they like. Unlike many private plans, the federal program doesn't cut benefits or raise premiums for people who retire.

The downside for former spouses of workers or retirees or their adult children, or people who quit government but want to keep health coverage, is that they must pay full premiums.

Employees and retirees on average pay about 40 percent of their total premiums. The government pays the rest, about 60 percent for federal workers and up to 75 percent of postal employee premiums. It works like this:

A government employee or retiree chooses, for example, the Blue Cross standard option. Its annual premium for single coverage next year will be about $1,760. But the employee or retiree will pay only about $440. The government will pay the rest.

An ex-spouse who has a qualified court order and meets other conditions could also enroll in the Blue Cross plan, or any other plan in the federal program. But the former spouse would have to pay the full yearly premium, or about $1,760.

A federal worker's (or retiree's) child turns 22. Unless severely handicapped, that adult child is no longer eligible for coverage under his or her parents' plan. Under new rules, that adult child may now continue coverage for 36 months by paying the full premium. 5 Years from Retirement?

If you are within five years of being eligible to retire, you should seriously consider joining the federal health program before the Dec. 10 deadline, even if you have better and less expensive coverage under your spouse's private health plan. The reason: You could lose coverage if you get a divorce. Or the private plan may offer inferior benefits, or no benefits, when either of you retires.

Federal retirees have the same coverage and premiums as workers. But to get coverage in retirement they must have been enrolled in the federal program for at least five consecutive years before retiring. To protect their status many nearing retirement age join a low-cost federal plan. Check with your health benefits office. Otherwise, you could wind up uninsured when you most need it. Insurance Advice

Health insurance expert Gordon F. Brown will be at the Interior Department auditorium today, from 11 a.m. to 1 p.m., talking about health insurance. The session is free and open to everyone. Disabled Employee Awards

The special presidential awards ceremony honoring outstanding federal workers with disabilities begins at 10:30 a.m. today at the Commerce Department auditorium. Marilyn Quayle, wife of the vice president, will be the keynote speaker.