Q. With the school season upon us, I'm concerned about the possibility of my two young children bringing home a case of head lice. Last year, there was an outbreak in their school, and it seemed to take forever to get it under control. If either of them did get it, what's the best treatment?

A. There are several treatments for head lice infestation. None is foolproof, but all will take care of most cases of head lice.

Head lice are tiny, blood-sucking parasites that pass from person to person through close contact, including shared use of clothing, combs and brushes. Head lice differ slightly from body lice and pubic lice, but all are medically known as pediculosis.

Head lice lay their eggs on hair shafts, usually within a quarter-inch of the scalp. These tiny white eggs, known as nits, hatch before the hair grows more than half an inch. Any nits farther than half an inch from the scalp are in all likelihood shells of eggs that have already hatched. They generally hatch within a week of being laid, but it may take up to a month after contact before any symptoms of itching begin.

If you discover head lice, there are several medicines you can use to get rid of them:

* Permethrin, which is found in Nix, a cream rinse available without a prescription. The cream is left on the hair and scalp for 10 minutes, then washed off. The treatment, which provides some residual killing action against the lice, works about 80 percent of the time. Because permethrin kills the eggs as well as lice, re-treatment generally isn't needed. As second treatment, however, will provide extra protection.

* Pyrethrins, which are found in Rid, A-200, R&C and End Lice. These over-the-counter shampoos or liquids are applied for 10 minutes and then rinsed off. They have no residual action.

* Malathion, available by prescription as Ovide. This pesticide appears to be the most effective lice-killer, but it had previously been voluntarily removed from the market because it had not been commercially successful. It has an odor, is flammable and requires a much longer application time than the over-the-counter lice products. Ovide needs to be applied to the scalp for 8 to 12 hours before it is rinsed out. It has the longest-lasting residual activity of any lice treatment--up to four weeks.

* Lindane, available by prescription as Kwell. This shampoo has fallen out of favor because in rare cases it can cause seizures in very young children. This complication usually results from excessive use or accidental swallowing of the lotion. Lindane shampoo is applied for four minutes, then washed out. It also appears to be less effective than permethrin, pyrethrins or malathion.

A few other pointers about head lice:

* Simple shampooing won't remove the nits. Even though the eggs are usually dead, they'll remain firmly attached. To remove them, use a fine-tooth comb designed to remove lice. Or you can try Nit Removal System, which has a liquid solution that makes the job easier.

* Careful combing and nit removal, a standard part of treatment, can also help prevent head lice from getting started. In fact, if you're able to remove all visible nits, chemical treatments for lice may not be necessary. It may be possible to treat the lice without using any chemicals if you're able to remove all visible nits.

* Family members and other people who have had close contact with someone who has head lice may need treatment. Soak combs and brushes in a lice shampoo or heat them in hot water (150 degrees) for 5 to 10 minutes.

Some lice have developed resistance to all of the available anti-lice products. If you aren't successful with one product, you may need to try another. And to avoid recurrences, you may need to re-treat after a week with whatever shampoo or lotion you're using.

Finally, some doctors have tried an anti-parasite antibiotic pill called ivermectin. This medicine is not approved by the U.S. Food and Drug Administration for lice treatment, but doctors may prescribe it if all else fails. Ivermectin kills the lice, but not the eggs, so you may need to take a second dose a week or so after the first.

For more information, contact the National Pediculosis Association (NPA), P.O. Box 610189, Newton, MA 02461. The association can be reached by telephone at 781-449-6487 and on the World Wide Web at http://www.headlice.org. The NPA recommends trying a special comb they sell to remove lice before resorting to any of the chemical treatments mentioned here.

Jay Siwek, chairman of the department of family medicine at Georgetown University Medical Center, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.

Consultation is a health education column and is not a substitute for medical advice from your physician. Send questions to Consultation, Health Section, The Washington Post, 1150 15th St. NW, Washington, DC 20071. Questions cannot be answered personally.