The Margaret Sanger Centennial Year has begun rather quietly, especially for so catalytic an agent of change as the woman who invented the very term "birth control." As H. G. Wells once wrote, "When the history of our civilization is written, it will be a biological history, and Margaret Sanger will be its heroine."

It was her intense commitment and energy that almost single-handedly promoted contraception in this country -- something that wasn't fully legalized until 1972.

Still it's hard to pin a nice unequivocal lable like "heroine" on the lady, even as a 100th-birthday gift. Her history is a whole lot more complex than that.

Sanger was born one of 11 children to an Irish immigrant free-thinker who sculpted gravestone angels. She began her career as a public health nurse on Manhattan's Lower East Side, where she became convinced that the solution to poverty was birth control.

In 1914, when Sanger was on the lam in London -- she had broken the pronography laws by distributing birth-control information -- she became an admirer of Havelock Ellis. Ellis was one of the more prominent eugenicists of the period, who applied (or misapplied) Darwinian notions to a creepy philosophy of selective breeding. He wanted only the "best people" to reproduce.

Under his influence, Sanger penned one of her early and least attractive slogans, "Birth control -- to create a race of thoroughbreds." Shades of the Third Reich. In fairness, Sanger didn't advocate birth control out of a desire to breed a super race, but made an alliance with eugenics out of a desire to push birth control. It was her one and only cause.

She came to believe contraception was a panacea. It would not only control poverty, end child labor and improve health but also give women "the key to the temple of liberty." Birth control would allow them to plan their lives without sacrificing their sexuality.

Despite her own support of what she saw as women's liberty, Sanger was hardly a favorite with the femisists of her era. Most of them looked at her rather ecstatic views on sex -- a "psychic and spirtual avenue of expression" -- with a jaundiced eye.

Suffragist Carrie Chapman Catt chided that "merely to make indulgence safe does not do enough." She and others were in favor of restraining male sexuality instead of freeing female sexuality.

Charlotte Perkins Gilman was uninterested in birth control because she thought that in an ideal feminist society -- like the one she described in "Herland" -- the energy of adults would and should be directed toward child-raising, not sex.

Still others, including many of the progressives, were sure that Sanger had the whole thing backward. She thought that large families were responsible for the evils of the system and that a wife could control the entire organization of society with a diaphragm. But the progressives thought the birth-control issue came in second, at best, to the issue of social reform.

By the 1920s and 1930s, birth control was overwhelmingly adopted by the middle class, not the poor. It was not accepted as a solution to economic injustice, but as part of the "sexual revolution" of the post-World War I period.

At that time the ideal of middle-class womanhood switched to the vision of a wife primarily as a companion and sexual partner, not as a mother. This was an overwhelming social change. For the first time, the credo, as author Sheila Rothman describes it, was marriage "based on passion, sexuality and, of course, birth control."

Margaret Sanger is not the first flawed "heroine" to facilitate a vast social change. Contraception, for all of its failures and problems, has enabled millions and millions of women as well as men to plan their lives as well as the size of their families.

But the most profound effect of the availability of birth control has been on the ability to separate sex from reproduction. This simple and revolutionary fact has been accepted by most of us with relief or joy or unease. The way we feel about the separation often underlies the attitudes we have toward the second sexual revolution, from extramarital sex to "The Joy of Sex" to the availability of abortion.

In that sense, this most fanatic and controversial woman was prophetic when she said that birth control demands "the frankest and most unflinching reexamination of sex in relation to human nature and the bases of human society." One hundred years later, this reexamination still goes on.