Q: My husband and I have decided not to have any children. We are considering either him having a vasectomy or me having my tubes tied. What are the side effects of these procedures?

A: It's a lot easier telling you the possible side effects of these two procedures than telling you which to have. That decision is a personal one based more on your convictions about childbearing and your marital relationship than potential side effects, which for both procedures are uncommon.

My first bit of advice is to consider vasectomy and tubal ligation ("tying" of the tubes) irreversible procedures. Even though with modern surgical techniques doctors often can reverse these operations, there is no guarantee beforehand that this will be possible. In that regard, you should consider the possibilities of separation, divorce or death of a spouse before making your final decision.

Vasectomies are done in the doctor's office under local anesthesia, so the risk of serious complications is very slight. The estimated risk of dying during the procedure is about one in 1 million. Complications include bleeding, infection and painful lumps in the scrotum, occurring in fewer than one in 20 cases. These are usually minor and treatable. Vasectomies fail to work in about one in 400 men.

Tubal ligation is the interruption of the fallopian tubes, which carry eggs from the ovaries to the uterus. This procedure can be done by cutting, clipping or electrically burning the tubes. Because it is done in the hospital under general anesthesia, tubal ligation is more expensive and there is a higher risk of complications, which include bleeding and infection.

On the average, chances of dying from the procedure are about one in 25,000, chances of a serious complication are about one in 50, chances of a minor complication are about one in 20. Tubal ligations fail in about one in 50 to one in 500 women. Ectopic pregnancy (pregnancy in the fallopian tube, which requires surgery) can occur after failure of a tubal ligation.

Once you've made a decision, both spouses should see the doctor who will be doing the procedure so you'll each know what to expect.

Q: I'm 38 years old, and about 20 years ago I was hospitalized with chest pain. My chest X-ray showed something abnormal, and eventually I had a biopsy done. The diagnosis was sarcoidosis. Since then, I haven't been bothered much by it. I used to get yearly chest X-rays, but I haven't had one in years. What is sarcoidosis, and could it have completely disappeared? Where can I get more information about this disease?

A: Sarcoidosis is something of a strange disease. Doctors don't know what causes it, don't understand what makes it get better or worse, and haven't found a permanent cure. It can act unpredictably, though in your case it seems to have been very mild and most likely has cleared on its own.

Sarcoidosis triggers the body's defense cells, called macrophages, to cluster into tiny clumps known as granulomas. This process touches off inflammation and scarring in different parts of the body, eventually leading to symptoms such as you've had. Often resembling tuberculosis, sarcoidosis most often attacks the lungs, leading to shortness of breath. It can also affect your eyes, skin, liver, spleen, heart, muscles and nerves. The disease usually starts in the twenties or thirties, affects women twice as often as men, and blacks 10 times as often as whites. Even without treatment, in many cases sarcoidosis clears within two to three years, though in some people it lasts longer and can seriously threaten their health.

Doctors often first suspect sarcoidosis from a chest X-ray, though a biopsy is usually needed to be sure of the diagnosis. Doctors sometimes use a blood test, known as ACE, and lung function tests to judge how active the disease is and how well therapy is working.

Steroids, such as prednisone, are the standard treatment, but they aren't without side effects, so doctors use them only when necessary.

For more information, write Sarcoidosis Family Aid and Research Foundation, 760 Clinton Ave., Newark, N.J. 07108; (201) 676-7901. Follow-Up

I was surprised by the number of readers who wrote in response to my recent column about skin chafing due to heavy thighs. All offered practical advice based on personal experience with this problem.

Several women said they were helped by wearing an undergarment, such as long-leg cotton panties or a split slip similar to pettipants. Another mentioned an undergarment named Chafeze, made by Warner's, and available in the lingerie department of Woodies. Apparently these undergarments tend to ride up. A neat trick to control this, one reader suggests, is to wear pantyhose over the undergarment.

One woman's mother "many years ago" had told her to use pure, clean lard. While I don't doubt that this helps, I'm not sure it's better than petroleum jelly or other skin moisturizers.

Other readers emphasized the importance of keeping the skin dry. One recommended splashing on rubbing alcohol after a bath or shower. Another uses a mixture of water with a little white vinegar after a shower, and follows this by drying skin creases with a blow dryer. The skin fungus that causes jock itch thrives in moist places, such as in skin folds. So if jock itch is a problem, keeping your skin dry helps to prevent it.