There are a growing number of families in the country operating under a contract. Not a marriage contract, mind you, not even a contract for housekeeping or cooking. The contract that they have signed is between teen-age kids and parents, and it's about drunken driving.

The idea was dreamed up and drawn up over a year ago in Massachusetts by some sophomores at Wayland High School, together with the town's health-education director, Robert Anastas. They formed something called SADD, Students Against Drunken Driving, and today that program can be found in more than 100 schools in Massachusetts and 350 more throughout the country.

At the crux of it is a deal struck between parents and teen-agers. The kids promise to call their parents "if I am ever in a situation where I have had too much to drink or a friend or a date who is driving has had too much to drink." The parents in turn promise to come and get the kids with "no questions asked and no argument at that time."

There is something hopeful about this unique negotiation. The parents who sign on the dotted line, after all, are not giving their blessing to booze. But they know the statistics of real life: 35 percent of the 25,000 drunk-driving deaths are caused by 16-to 24-year-olds; 55 percent of all traffic deaths are due to alcohol.

Given the alternatives--and sometimes that's all parents of teen-agers are given--they choose to protect their kids from the worst consequences of their mistakes. They say that there's a difference between breaking a rule and wrecking a car. They promise to suspend criticism for the moment and help.

I'd like to think that this SADD creation could be a model for families. I can imagine a file full of such contracts for teen-agers and parents: "We don't want you to drink. But if you do drink, for heaven's sakes, don't drive. We don't want you to smoke marijuana, but if you do, don't get hurt. We don't want you to have sexual intercourse, but if you do, don't impregnate or get pregnant. We may not approve, but we'll try to be there for you."

I thought of the "sex contract" especially last week, when, as a parting shot, Secretary of Health and Human Services Richard Schweiker decided to publish rules that would force federally funded birth control clinics to tell parents when girls under 18 get birth control prescriptions.

For two years, the administration has tried to sell this idea as an aid to families. It would be a government "contract" to make the clinics tell, even if children won't. The government would put the dime in the phone booth, the stamp on the letter.

This law, this "squeal law" as it's been dubbed, has a certain appeal. There are times when parents long for information about the young people in their lives. But in real life, it cuts against their grain, against their goals.

The statistics of teen-age sex are as well known to parents as the statistics of drinking. By age 18, two-thirds of the boys and more than half of the girls have had intercourse. The threatening accident at this human intersection is pregnancy. There are 1.2 million teen-age pregnancies a year.

If the main goal of parents is what I think it is, protection--helping their own through the minefield of adolescence--then this law would leave the young more vulnerable. Of 400,000 teen-agers using these birth clinics, it's estimated that a fourth would no longer come for help if the clinics had to tell on them. Only 2 percent would stop having sex.

The reality is that parents are often faced with alternatives they haven't chosen, alternatives they may not like. They are constantly pushed back to the second line and third line of defense. They can't ultimately choose whether their children have sex, whether their children confide in them. Sometimes the choice comes down to this: is it better for those young who can't tell their parents they're having sex to have it with, or without, birth control?

I just don't think that government contracts work in the family arena. I like the SADD model better. It's the personal contracts that count, the private ones that we write as volunteers, and sign as partners. But even these can only work when families can talk about sex as freely as they are talking now about drinking and driving.