Q: It was nearly two years ago that you told a 16-year-old girl about sex and what she should consider. Although I only have boys (three), I clipped your column for future reference. Could you write a similar one about boys?

A: It would be easier to walk through a mine field.

Parents and teen-agers can say all they want about the equality of the sexes--and how the values for one are the same as the other--but parents never call a promiscuous boy promiscuous and teen-agers don't either.

Nor is sex the same for a boy and a girl; she can't walk away from a pregnancy.

And then there is the old-fashioned verbal legacy that a boy and a girl inherit. What is a gain to him is a loss to her. When a boy has relations for the first time, he is not only proud, he is elated: He is a man. He also is the envy of his set.

When a girl has relations for the first time, she often hesitates to tell even her best friend. In the jargon of yesterday--and today--she has lost her virginity. To a girl under 18--and to many who are older--this loss can bring a sense of shame and guilt that may continue for years, no matter how much the girl and the boy love each other. This is magnified if the act was impulsive or committed under the influence of drugs or alcohol, or if the partner was just a casual friend.

There also is a great loss of self-esteem if the girl was not gratified. Since a teen-age boy has a bit to learn about lovemaking, sex often can leave the teen-age girl feeling still more unworthy, for she's sure she must be frigid.

You'll want your sons to know that sex, to be its best, is the result of a long and loving relationship. It takes a commitment to sustain the many stresses a sexual relationship brings. Otherwise sex erodes love if the practice begins too soon and damages integrity if there is no love to bind it.

Sex is based on the same emotions for boys as for girls. The passion, the joy, the caring are alike--and so are the responsibilities. Although the differences in attitudes and heritage still linger, the guidelines for the boy have changed. Now he must feel enough love to stand fast and enough loyalty to stand by.

The boy must realize that he is 100 percent responsible for his role--just as the girl is 100 percent responsible for hers. He not only must take her feelings into consideration, but he must know as much about birth control as she does. For this he relies not on his friends or even his parents (there's too much misinformation around), but on an authoritative, up-to-date book and the prevention it recommends.

He also must know he has to forgo sex if he thinks he might have picked up a sexually transmitted disease, like herpes or gonorrhea. To pass it on would be, to say the least, ungentlemanly.

He also must be willing to fulfill his role if a pregnancy does occur--since he is just as responsible for it as she--and to take part in the awesome decision to abort or deliver.

Abortion is as agonizing a decision for him to make as it is for her. If they should decide on abortion, he will never be quite the same again, and he should know that. He also will have to pay half, if not all, of the cost; be with her for the operation and take part in the counseling, before and after.

Delivery requires another kind of support, again both emotional and financial, from prenatal care to the birth itself. There are other decisions he must make. Adoption is a wrenching one, and marriage can be overwhelming.

When marriage is begun too soon, education usually is ended too soon, and the consequences can be grave. They are almost as serious, however, for the father if they don't marry. Besides a lifetime of regrets, he is--and should be--legally responsible for half of his child's support for 18 years and morally responsible for whatever emotional support he is able to give, according to the wishes of the child's guardian.

Nothing tests a teen-ager's maturity quite so much as sex, except perhaps the absence of it. The supervision of adults and activities help him say no, but basically a boy must decide for himself when he is man enough to live with the consequences. Sex is too important to turn it into an experiment, and besides, that doesn't work. Once tried, it's a tough practice to quit.

You and your sons will get some provocative information about teen-agers and how they think and act in all the serious areas--including sex--in a valuable book called The Private Life of the American Teenager by Jane Norman and Myron Harris, Ph.D. (Rawson, Wade, $14.95). The report is distilled from 160,000 interviews with teen-agers.

Another book, Don't Worry, You're Normal by Nissa Simon (Crowell, $4.95), will give teen-agers candid, objective information on sex, drugs and peer pressure, as well as development, nutrition and emotional concerns. Both books belong in any household where there is a teen-ager.