How do I go about gaining weight? I'm healthy, but I've always been too thin and have never been able to add and maintain the few pounds I think would make me look better.

ANSWER - For those who are naturally very slim, gaining weight is often quite difficult. The task isn't made any easier by the lack of sympathy accorded them by others with the reverse problem.

In barest terms, the solution is simply to increase portions a bit at mealtimes and to add two or more snacks during the day. For instance, you could have a small muffin and pat of margarine as a midmorning snack. At midafternoon break, you could snack on a fruit yogurt and some crackers. In the evening, before going to bed, try having an ounce of cheese, some crackers and a piece of fruit. Depending on the size of the servings, these few additions would total somewhere between 600 and 750 calories. When you've added an excess of about 3,500 calories to your usual intake, you should see the reading on your scale rise a pound.

The amount of food you can add comfortably varies from person to person. What we've suggested are general guidelines that you can adapt to suit your own needs. Of course, it's a good idea to increase your calories with nutritionally sound food choices rather than foods containing fat, sugar and little else.

A mistake commonly made by those trying to gain weight is to increase the size of the snacks too much. Then when mealtime comes around, they're not very hungry. Without realizing it, they eat less. That quickly undoes the effort targeted at adding extra calories.

Keep in mind that the rate of weight gain can vary. Don't get discouraged if progress is slow. Be consistent and you should see some results.

QUESTION - My elderly aunt developed diabetes several years ago. Unfortunately, she didn't take care of herself the way she should have. She's overweight and has just been put on insulin. Now, however, she is motivated to pay more attention to her health. Can you recommend an easy-to-understand reference for her?

ANSWER - A volume now in its fifth edition, written in fairly large print and bold type, may be just what you're looking for. "Diabetes Mellitus: A Practical Handbook" by Sue K. Milchovich, R.N., B.S.N., C.D.E. and Barbara Dunn-Long, R.D. (Bull Publishing, $10.95) covers the waterfront of information a diabetic should know.

It first provides the reader with a basic understanding of the disease, then goes on to discuss many aspects of the diabetic diet, including the Exchange System, eating in restaurants, and use of alcohol and diabetic foods. It explains both home blood-sugar and urine testing, administration of insulin, oral medications, personal hygiene, and skin care, and addresses other topics of interest to diabetics.

If your aunt has had trouble adhering to a diet and losing weight in the past, we suggest you encourage her to visit a registered dietitian to obtain firsthand guidance in diet management. But as a backup reference, this little book is a top-notch choice.

QUESTION - I love pork, but I always worry a little when I cook it. I've heard conflicting information about exactly how hot a pork roast must be for it to be safe. Can you tell me?

ANSWER - Here's what the USDA recommends: Pork roast should be cooked to an internal temperature of 160 degrees Fahrenheit, which is a medium-done stage, or up to 170 degrees for well-done meat. This is somewhat lower than the 185 degree temperature that had been recommended for many years; perhaps the change has brought confusion.

However, given the fact that studies have indicated that trichina were killed when meat cooked in home ovens reached a temperature between 130 and 140 degrees, the new recommendation certainly allows a measure of safety. Curiously, a recent study of consumer preference conducted by researchers at Iowa State Association found that while most consumers preferred meat cooked to 160 degrees, some actually preferred meat cooked longer, sacrificing juiciness for what was perceived as increased flavor.

1991, Washington Post Writers Group