Civil servants worrying about things to do before Christmas have only a short time left to persuade their government backed health insurance plans to pay, or help pay, for:

1) Sex change operations.

2) Silicone breast enlargements.

3) Birth control devices.

4) Orthopedic shoes.

5) Meals for friends who visit them while they are hospitalized.

Those are a few of the items that will be excluded from all or most 1978 health insurance plans that provide coverage for the 3.2 million U.S. and postal workers, and retirees, in what is billed as the world's largest "company" health program.

As announced last week, many of the 66 health insurance carriers in the federal program will be making changes for 1978. Most will raise rates. A few will lower, or keep them at current levels. Many will add new benefits. Nearly all will close some embarrassing medical and legal loopholes by saying, quite specifically, what they will not - and never intended - to cover.

Federal officials and insurance company executives say they have no way of knowing how many government employees have asked for financial assistance in sex transformations. Nor do they know how many were successful in getting that help, since the information is protected because it involves medical or psychiatric data that is confidential.

People have been asking their insurance companies for help along the above-mentioned lines. And when the government and the carriers negotiated contracts this summer, for the 1978 year, they dedided it was important to draft a uniform code of exclusions, so people would know what NOT to expect.

In addition to the exclusions already detailed, some of the plans - to bring their practices in line with others in the government program - will limit cosmetic surgery to correct birth defects to persons under age 22. Formerly, some of the plans had no age limits.

Others will drop payment for weight control treatments when the obesity is not caused by organic condition, no longer pay for reversals of sterilizations, stop letting people charge for rented TVs in hospitals, or for heating pads.

Some of the carriers will continue to pay for birth control pills, others will not. Some have expanded the area of noncoverage to include all "birth preventative" devices.

A few will expand dental coverage while other plans will no longer pay for the "proper fitting of dentures," which, for them, in 1978 will become an out-of-pocket expense.

Some carriers still provide coverage for orthopedic devices, but some that never did, and some who had to pay for them because they did not specifically exclude them, will tell people that for the 1978 year.

"This is a tough thing to discuss," and insurance official said, "because we don't have any way of knowing - and I'm not sure I'd want to find out - if we have had to pay off on some of these things. I know there have been requests for sex transformations and for all I know, some have been paid for psychiatric reasons.

"What happened is that we decided to have uniformity, where possible, in exclusions and to make clear to people what they could not expect to be covered."

"Let me reverse the question," he said. "You were out sick a couple of weeks ago. What was wrong with you?" I told him it was none of the 5 reasons listed at the beginning of the column, probably just a touch of the flu. "There you are," he said. "Medical information is private. It should be. That is why we don't know, and couldn't say if we did, about requests for sex change operations and things like that."

To find out what they will be paying for - and what they will not be getting - federal workers should consult the health insurance brochures available in most personnel offices, or health rooms. Employees will have an open season period between Nov. 14 and Dec. 9 to make changes in plans or coverage. It would pay to read the brochures this year.