IT IS NOT very often that a columnist can claim expertise on a specific subject. We are, after all, supposed to be generalists, and for this reason we know, to paraphrase the old song, a little bit about a lot of things, but not enough about one thing to be a specialist. This is not true, though, when it comes to chaste teen-agers. I was one.

I was a chaste teen-ager from the age of 13, when I became a teenager, to the age of 20, when I was no longer either a teen-ager or chaste. Time took care of the former and a girl named Lenore took care of the latter sometime in my 19th year. She went on to become an anthropologist. I think she looked at me the way Margaret Mead looked upon the Samoans.

At any rate, my experience as a chaste teen-ager is now relevant because chastity among teen-agers is now being promoted by Sen. Jeremiah Denton (R-Ala.), who thinks it is a good thing. Since there are almost no chaste teen-agers anymore, I will give the good senator the benefit of my own experience.

Nothing encourages chastity like acne. A good pimple in the corner of your mouth can keep you chaste for months. All during this time you will be told that the cure for acne is to get unchaste as quickly as possible, something that cannot be done as long as you have acne. This is known as a conundrum. It is also good preparation for life.

Brown shoes almost guarantee chastity. In my experience, everyone who wore brown shoes was chaste. People who wore brown shoes and white socks were not only chaste, they probably still are to this day.

Ear muffs also encourage chastity. So do galoshes and mittens as opposed to gloves. Taking your lunch to school helps chastity. So does having a lunch box, a pencil case and one of those little things you put in your breast pocket to hold a pencil. No one who ever wore one of those things was anything other than chaste. This is a fact, and the government should issue all of these items to kids at school.

There is some feeling that to be a chaste teenager is a wonderful thing. Why that is, I do not know. I do know that as a chaste teen-ager, you spend much of your time attempting to remedy this situation. This means that you do not do your homework or your schoolwork or anything else that will interfere with your single-minded attempt to get unchaste as soon as possible.

Chaste teen-agers are always thinking of chastity, unchastity and allied subjects. I can tell you on the basis of my experience when they think of these matters. They think of these matters while getting dressed, brushing their teeth, eating breakfast, going to school, in school, in the cafeteria, in study hall, in class, while going home from school, at dinner, while pretending to do homework, while on the phone, while getting undressed for bed, while brushing their teeth, while getting into bed and while trying to fall asleep.

Unchaste teen-agers, on the other hand, have time for extra-curricular activities. They do their homework and they study well in school and they sleep better at night. They are, on the whole, better adjusted, happier and less obsessed with the idea of chastity than teen-agers who are, bless them all, chaste.

I will tell you some of my other secrets for keeping chaste until the age of 19. Don't call girls for dates until Thursday. This almost always works since almost all girls who are unchaste have already been booked for the entire weekend.

Date girls with parents who stay up very late and who make lots of noise in their sleep. Date girls whose fathers have a habit of coming down the stairs after midnight and who say, "Oh, I didn't know you kids were back."

Use only public transportation on dates. This is a sure-fire method to encourage celibacy since it not only takes two people to have sex, it also takes a car. It is for this reason that New York City, where many people don't have cars and rely on public transportation, is the most chaste city in the country.

Talk a lot about respect.

Have freckles.

Have red hair and freckles.

Take a friend with you on dates.

Date girls with large, protective dogs.

Date girls named Norma who have skipped a grade.

Don't date girls named Lenore.