Like those in all good magazines, letters to the editor of Ms. tell a story. This has been so thoroughly and spiritedly the case that, for its 15th anniversary, the pioneering magazine of the women's movement has collected the best of them in a new book, "Letters to Ms., 1972-1987" (edited by Mary Thom and published by Henry Holt).

The August issue of the magazine itself, with its stock-taking theme, carries a batch of solicited comment from readers on the general topic: what Ms. and the women's movement have meant to me. Two of them provide an apt point-counterpoint at this anniversary juncture.

A teen-ager in Nebraska writes: "My mom is pretty much a liberated woman, and she has made me more of an independent person ... She makes me do things for myself. I think it's going to help me a lot when I'm in college or living on my own. I think it will probably help me to have a better marriage. I'm not going to be asking the girl I marry, 'Do this for me. Do that for me,' because I can do pretty much anything that a woman can do in the household."

On the other hand, to one agitated Florida correspondent, "Feminism has also made me ashamed to say I'm just a secretary. This is good, honest work, yet I hope when my child is grown to maybe have the opportunity to go to school and pursue a 'real' career ... God, how embarrassing to be a secretary at my age -- never mind that I'm very good and have supported myself and my child. I haven't had time to become a star."

'What More Do Women Want' Founding editor Gloria Steinem, in her introduction to the anniversary issue, acknowledges that the magazine has recorded an astonishing period of collective strength and individual self-realization for American women -- and of enlightenment for those around them, as the first letter attests.

But Steinem wants to remind anyone who says "Enough!" -- or, to amend Freud's phrase, "What more do women want?" -- of what she believes are "the realities of most women's lives: the wildly disproportionate amount of violence directed at females because they are females, the 'feminization of poverty' that simply means most of the poor are women and kids, the killing sexism still taken less seriously than racial or religious bias that affects men, too, the double dose of prejudice against females who are not white, not heterosexual, not able-bodied, or not young."

Or not engaged in suitably impressive careers: to her list Steinem might have added the condescension of some -- Ms. readers undoubtedly among them -- toward the likes of the second letter writer. In a tough-minded essay called "The Next Wave," Barbara Ehrenreich makes the point explicitly, acknowledging that feminism has been a middle-class phenomenon and that its leaders have been known to rest on the insufficient laurels of 15 years. "Even this magazine has been accused, not entirely without justification, of a mellowness unbecoming to its adolescent years," writes Ehrenreich.

From its birth as an insert in the pages of New York magazine, Ms. has been for, about and of a movement. And it remains today what it became very quickly after its founding: (1) accessible, mainstream journalism with (2) a point of view, (3) plenty to write about, (4) an identifiable constituency and (5) enough money, at times just enough, to survive.

Most magazines you see these days can only claim two or three of these desiderata, if they are lucky. The other big -- mostly much bigger -- women's magazines lack (2) and (3), but if their readers are unhappy, they are not letting their money talk. McCall's, Family Circle and Woman's Day each has more than 6 million paying readers every issue, Ladies Home Journal more than 5 million and Redbook more than 4 million.

Ms. and Its Sisters Ms., for its small part, has fewer than half a million readers. Yet it can be said that its influence on what women read has been out of proportion to the number of women who read it -- in the power of its example and ideas on other magazines.

Most directly, Ms. cleared a path for such successful crypto-feminist monthlies as Savvy, Working Woman and Working Mother. But its agenda, over time, also has penetrated the relentlessly static list of stories that the traditional women's magazines publish month after month, year after year.

Without abandoning heavenly recipes for deviled eggs, beating the frizzies and 10 tips for flatter tummies, the so-called Seven Sisters now attend -- usually in the same breezy voice -- to the plight of the latchkey child, demystifying the orgasm, and six ways to win at office politics. And in the back of these magazines, Cheez Whiz coupons and ads for depilatories are side by side with credit card applications and ads for condoms.

Ms. deserves some thanks for identifying, and even abetting, the current audience for all women's magazines. (A related but somewhat different compliment probably can be paid to Helen Gurley Brown's adventurous Cosmopolitan.) And of course Ms. would not have survived, and its big sisters would not have cared, if their readers hadn't glommed onto what the women's movement has been about all along. Successful magazine publishing is trickle-up, as must be appallingly obvious at the newsstand.

In her essay, Ehrenreich contends that "the key to a feminist renewal" lies in a movement led by the working-class woman, who "is still pretty much where she always was: waiting on tables, emptying wastebaskets, or pounding a keyboard for an hourly wage ... When she looks out -- at television or the dressed-for-success-style magazines -- she sees more fortunate women bounding ahead. But when she looks around her, she sees women like herself, going nowhere."

And except in rare cases, probably not reading Ms. The movement Ehrenreich describes, if it emerges in any palpable form, will need its own magazine. The question energizing this 15th anniversary issue of Ms. is whether it can become that magazine, by reaching out to the woman Ehrenreich calls "perhaps a fellow-traveler but never an actual feminist." Or whether magazines like McCall's and Redbook, nonthreateningly and almost imperceptibly, are doing the job already.