Q. "I just read your article on sibling rivalry and how children fight for a parent's attention," writes a Silver Spring mother.

"But answer this question:

"What happens when the two siblings are a boy, or should I say 'man' of 19, and a girl, age 15, and they still scream and hit each other?

"What does a mother do after she has exhausted every piece of advice given or written about this problem? What does a mother do about the effect if is having on her own personal health, both mental and physical? What does a mother do when the stepfather says he will not get involved with the problem?

"Aside from running away from home -- what does a mother do?"

A. What a tragic place you find yourself in, and yet, the appraisal for the Seven and a Nine still holds: Sibling rivalry is a bid for attention, but this one has gotten far, far out of hand. Serious measures are required.

Your children have no right to treat each other like that and they have no right to treat you like that either.

You must have asked yourself 1,000 times what each child does to invite these fights. And now for that knife-in-the-gut question that's so hard to ask: What do you do to invite it?

Although your children are responsible for their own behavior (absolutely), you also are responsible for yours.No one can be in a relationship without inviting a response, good or bad, and you want to probe your soul to see how you encourage their tantrums.

You're bound to be throwing out signals before a word is ever said, walking on eggshells around them, bracing your body when they are in the same room. Your children are sending out messages, too, and even your husband, sitting on the sidelines, is in his own way fully involved.

People spoke with their bodies eons before a language was invented and these messages are still much louder than words. Any anger, any fear you feel is going to belie you voice, however soft and measured it is.

You can't stop these scenes until you get rid of your own well-justified hostility, and you're only going to do that when you decide that you come first. You can't get there all by yourself.

By now the people you love best have squelched your feelings until you wonder whether you have any rights left at all.

You need to pour your heart out to a therapist -- a psychiatrist, a psychologist or a psychiatric social worker -- who can help you get your self-esteem back again and help you peel your own personal onion.

This is the person who will both comfort you and confront you, paying such close attention to what you say that you can't slip away from a sticky point.

Only when you have talked out your fury and your despair will you be able to listen to anyone's advice, for anger blocks the eardrums like great wads of cotton.

In the process of this therapy you'll be able to replay those scenes and figure out what could have happened if you had reacted a little differently. If you can defuse the tense situations, you will be able to give more positive attention, which is what you children both need.

Ideally, the therapy would include family sessions -- with your husband -- and your children would have some individual therapy, so everyone could learn how to deal with their anger constructively. You have to remember that anger is only a bad feeling if it's expressed badly.

Certainly it would be foolish to pretend that people don't get mad, or have the right to get mad; they just shouldn't hurt others in the process.

If your children don't learn that abuse -- physical or mental -- has no place in a relationship, they're going to carry this behavior into marriage and parenthood.

Your children also need to have full physicals -- if you haven't done this already -- to see if there might be a neurological, metabolic or allergic problem that triggers outrageous anger in one, to which the other has always reacted. This kind of a check-up should precede any psychiatric treatment.

You also will profit by a couple of books to help you decode your children and give you courage to stand up to them. One is new, called "Raise Your Kids Right," by Dr. Lonnie Carton (Putnam, $9.95).

The other is an oldie, and still one of the best, "Your Child's Self-Esteem," by Dorothy Corkille Briggs (Doubleday, $3.95). Even though it has a picture of a baby on the cover, its examples and explanations are helpful at any age.

There are also two self-saving steps to take. They begin when you tell the family -- at some quiet time -- that you are going out at the first sign of another tantrum, and invite your husband to go along.

And when the scene happens, grab the car keys, stop whatever you're doing -- whether it's cooking the meal or mowing the grass -- and go, with or without your husband. No threats, no hanagues, just be gone within five minutes. And if you don't have a car, walk.

Go to the movies, go to dinner, but go. You might have to keep some money hidden just for that, or you might go without dinner, but it's better to sit alone in a park for two hours than be a party to you children's hysteria.

You can call it running away if you want, but we call it self-preservation.

And if the tantrums are still as frequent in a few months, then it's your responsibility to tell that 19-year-old that no matter who starts the next one, he is an adult and it will be his turn to go -- permanently -- even if he has to quit college. He will never be a man if he can't learn to live by the consequences of his acts, and in this case, if he can't live by the rules of the house, he can't live in it.

You still must care for your daughter, as a minor, but the minute a child is out of high school a parent's duty is done. Anything you give afterward, including room and board, is just that -- a gift -- and the child who wants to spurn it should get no more than a big good-bye.