This is the sort of column that is supposed to begin with the words, "I'm not a prude, but . . ." However, I'm not so sure anymore. I think I'm becoming one of those little old ladies in tennis shoes who go around brandishing umbrellas at X-rated people.

I realized it first in one of those boutiques where people try on clothes to a disco beat. But this time, the stereophonic sound wafting over the racks resembled the sound track of a porno flick in which the lead female says nothing but "Oh, Oh, Oh." It made disco seem subtle.

What I wanted to do was walk up to the manager and tell him that if he didn't switch off the hard-core station, I'd walk out the door. What I did, however, was walk out the door.

Then, a few days later, I personally girl-cotted Jordache jeans from my daughter's dressing room, because of the ad they have running. This ad features a teen-age girl mounting a teen-age boy, piggyback style. Jordache has brought the values of Lollytots magazine into such a good gray publication as the Sunday New York Times. I personally refused to support the kidporn of the ad world.

As if this weren't enough, last night I found myself ranting and raving about the Calvin Klein TV ads that pan slowly up to the crotch of 15-year-old Brooke Shields and say something like, "I have 15 pairs of Calvins in my closet. If they could talk, I'd be in trouble." Suddenly I wanted to drown Brooke Shields in the nearest blue lagoon.

Once upon a time, it was only card-carrying members of the Legion of Decency who went around sputtering words like "disgusting," "obscene," "indecent." But once upon a time, a prude was someone who knitted clothes for dogs. Once upon a time, "indecent" was the word for a wife who undressed in front of her husband with the lights on.

Now I find myself applauding a friend who got two underage kids kicked out of the R-rated "Dressed to Kill."

You don't have to be a parent to be appalled at the teeny-bopper stations playing the 10-minute orgasm, or the clothing industry marketing 15-year-olds into sex-for-sale objects. But it helps.

Growing up, especially in the second decade of life, is mined with explosive changes, physical and emotional. It's the time when young people are supposed to gain competence, to learn who they are in the world and how they'll survive.

It's an even tougher business today when kids are unemployed and kept in age ghettos of schools. The teen-agers I know are often acutely aware that they are regarded as useles, if not downright dangerous.

There is no way for them to test living skills. The rites of passage have been reduced to drinking, driving and sex. The only value they seem to have is as consumers. So they are being, quite literally, sold sex aong with their deodorant and shampoo and eyeliner and movie stubs.

The contradictions are really stunning. Television is filled with alarmed programs about teen-age pregnancies -- and sponsored by the sex merchants. The movies show Foxes and Little Darlins doing it "naturally" in Blue Lagoons or Caddy Shacks, while the marquees suggest "parental guidance" or an 18-year-old chaperone.

The worst part of the sex mania is the message -- as one-dimensional as the one I heard on that record. There is little aura of kindness of awakening sensuality. There is virtually no sex on television that isn't sniggering or exploitive, bumps or grinds.

As parents, many of us try to spoon-feed our children messages about the human context in which we live our sexual lives. Meanwhile, they stand hip deep in televised "jiggle" jokes and X-rated "acts." Like some complicated sauce, sex is reduced, over the media flame, to "doing it."

For too long the people leading the protest have been the sort who want to ban D. H. Lawrence and repress sex back to a necessary evil. As a First Amendment junkie, I defend the right of consenting adults to read and behave as they will. But I don't have to like the messages or ignore the marketing of sex, especially to kids.

I can rage against it. And if that makes me a prude, pass me the umbrella.