Q: Several years ago, the idea of considering catsup as a vegetable in the school-lunch program caused a furor. Since then I have heard catsup indicted as a source of too much sugar and salt. What are the facts?

A: First, the sugar: A number of sweeteners may be used in commercially prepared catsup. They add up to more than half a teaspoon of sucrose per tablespoon of catsup and account for more than half the 16 calories in a tablespoon of catsup.

As for salt, the same amount of catsup contains about 155 milligrams (mg.) of sodium, a little less than in a tablespoon of mustard and a bit more than in the same amount of pickle relish.

The important point to remember about the calories, sugar and sodium in these condiments is that many people use a lot more than a level tablespoon at a time. If you consider three tablespoons not an unusual amount, the picture changes. That portion would provide as many calories as a serving of many fruits and vegetables, both of which provide considerably more nutrients. And it would add about a quarter-teaspoon of salt to the diet.

Q: I have two questions about chocolate. What causes the whitish discoloration that sometimes appears on the surface? And what is white chocolate?

A: There are two reasons that chocolate gets that whitish coloring. It may be "fat bloom," which is nothing more than cocoa butter that has left the crystallized chocolate mixture and migrated to the surface. That type of bloom tends to occur most readily at around 70 to 75 degrees Fahrenheit. "Sugar bloom," the second type, can occur when loosely wrapped chocolate is stored in the refrigerator. Moisture condenses on the surface and sugar from the chocolate dissolves in it. When the moisture evaporates, it leaves behind a white crust of sugar crystals.

White chocolate is simply a mixture of cocoa butter, milk solids and sugar. It contains no cocoa solids. White chocolate is especially popular in the summer because it does not show the changes that occur in regular chocolate. But, it turns rancid more quickly.

Q: It is often said that Americans take too many vitamin pills. Are there any data to support this claim?

A: The Center for Food Safety and Applied Nutrition of the FDA recently reported results of a national telephone survey of adults 16 years and older conducted in 1980. It found that, excluding pregnant and lactating women, almost 40 percent of the population regularly consumed one or more supplements. Of those, over half consumed just one supplement, while almost 11 percent swallowed five or more, up to a maximum of 14. As in earlier studies, the study found that average consumption was higher in the Western states. Use of supplements was more frequent at incomes over $25,000. Women of all ages took more vitamins than men.

You might expect that a single multivitamin would be the supplement used most often, but this was not the case. The "single vitamins miscellaneous dietary component" category -- which included single vitamins as well as choline, PABA, inositol, lecithin, bioflavinoids, betaine and amino acids -- was the most widely consumed product, taken by 17.3 percent of the population surveyed and 45.2 percent of supplement users. Vitamin C, either alone or in combination with other nutrients, was the most widely consumed nutrient, taken by more than 90 percent of supplement users. It was followed closely by some of the B vitamins.

Various mixtures including multivitamins, multivitamins and minerals, and multivitamins with iron were used by 12.4 percent of the population and 32.1 percent of those who took supplements.

One important question is how many Americans consume dangerous amounts of vitamins and minerals. This study did not explore that issue in depth. However, the investigators did find reason to be concerned about high levels of supplements taken by some segments of the population. They have made their data available to other researchers who might want to examine this and other issues further.

Meantime, the basic fact remains that, unless otherwise prescribed as part of a medical regimen to treat a specific condition, supplement use should be limited to a multivitamin containing 100 percent of the Recommended Dietary Allowances. For women during their reproductive years, many physicians suggest that the supplement also contain iron.