For those of you who missed it, Sophia Loren turned 50. We are told that she celebrated her birthday publicly in a shopping mall in Atlanta. What glamorous errand had brought the Italian movie star to the mall? Had she run out of candles or pantyhose?

No, Sophia Loren had joined the bustling ranks of certifiably older women promoting beauty. By now it appears that nearly all the women who are pumping and primping, selling their shapes and their books on the circuit, are more than halfway through the average life expectancy.

Only last year Joan Collins, 50, wrapped her body in nothing but boas for Playboy. Before that Jane Fonda, 46, began bumping and grunting on thousands of videotapes. Now we have Raquel Welch writing and posing as a 44-year-old yoga pinup queen and Sophia Loren hustling for Coty and a book of beauty tips. Middle age is so popular that soon a younger woman may have to lie to get a publisher, or endorse a face cream.

Frankly, I don't begrudge Jane her biceps or Joan her pectorals or Sophia her everything. By all accounts, women like these are supposed to offer hope for the Ghost of my Christmases Future. But I'm not sure how I feel about their kind of middle age.

When I was a kid, the only older women who won prizes for their physical preserves were Greta Garbo and Marlene Dietrich. Even they were looked upon with suspicion, as if there were pictures of Doria Gray hung up somewhere in their closets. Most of us assumed that at some point past 30, you just quit. It was a vaguely unsettling but also reassuring idea.

After all, it was hard enough trying to look like a model in Seventeen when you were a teen-ager. How many of us suspected that we would be compared to Linda Evans at 40? Indeed, think of the women who have spent five decades being measured against Sophia Loren. Is it any wonder that they are fans of Elizabeth Taylor?

The central notion of the middle- aged, show-and-sell routine is that if she can look that good at 50, so can you. Just follow the directions on the package or the book. This is a bit like saying that if Shirley MacLaine can dance at 50, you can dance at 50. (Dear Diary: Can I look like Catherine Deneuve at 41? Dear Writer: Did you look like Catherine Deneuve at 20?)

The sales pitch of beautydom is generally accompanied by a charming disclaimer about youth. Loren, for example, writes in her new book, that "this mature approach to beauty . . . does not depend on possessing the dewy cheeks of a teen-ager." The secret in this advice is that Sophia Loren apparently had "dewy cheeks" as a teen-ager. The rest of us had zits. A few of us may have had muscles in youth; the rest had premature cellulite.

The new role models of midlife assure us that they, too, were really awkward and unattractive in their youth. "I wasn't always considered beautiful," writes Loren. "When I was 13, my nickname was Toothpick." Raquel Welch goes a bit farther, saying, "For the most part I see myself as a well-proportioned wimp."

But if you really think of Loren as a toothpick and of Welch as a wimp, then I have some books, a line or two of beauty products and a lot of exercising just waiting for you.

As far as I can tell, not one of the new breed of midlife beauties is going to make their peers feel good about themselves. It's Rosemary Clooney in a muumuu who makes them feel good. What Loren, Fonda, Welch, etc., have done is to raise the threshold of self- hate faster than the age span.

We no longer look forward to letting go at 30. There is no thought of aging gracefully at 40. At 50, we are faced with a prospect of daily regimens to soften our skin and tighten our thighs. The end result of all this is that those of us who failed to look like Brooke Shields at 17 can now fail to look like Victoria Principal at 33, like Linda Evans at 41 and like Sophia Loren at 50.

When Gloria Steinem turned 50 this year, she updated her famous line from 40. She said, "This is what 50 looks like." With due apologies to the cult of midlife beauty, allow me two words: "Not necessarily."