"I'd have been as dead as a doornail in the 17th century," says Lady Antonia Fraser cheerily, reflecting on the difficult birth of her fifth child. "I had six children in 10 years. For them it would have been nothing. They all did it." Lady Antonia knows whereof she speaks. She is in this country to promote "The Weaker Vessel," her fifth major work of history, which recounts the intimate daily lives of women in 17th-century England.

The 52-year-old Lady Antonia is not, to put it mildly, a weak vessel. In her hotel suite ("So much more luxurious than our home"), she is charming and controlled. Her impeccable manners make the impersonal surroundings welcoming. Her husband, playwright Harold Pinter, moves quickly through the room as if in fear of attracting a stray question or two. He's here to read from his plays at the 92nd Street Y. "He's going to act every part himself," his wife explains. "Something he's always wanted to do."

And that's all about Harold. Lady Antonia is legendary for her refusal to answer questions either about her husband or about the highly publicized scandal that preceded their marriage. In 1975, Pinter left his actress wife Vivien Merchant, and Lady A. left her politician husband Sir Hugh Fraser, the father of her six children. The London tabloids had a field day, though such a furor is hard to reconcile with this small man in his dapper gray suit and horn-rimmed glasses and his stately blond wife.

On this occasion Lady Antonia does unbend to relate, with obvious delight, the story of her husband agreeing to give a quote about her to a journalist. To the dismay of the writer, the long-awaited quote was, "She's terrific." The reporter, though, persisted. "She's terrific in every way," allowed Harold Pinter when pressed. His wife was enchanted. "Harold's Harold," she explained. "He does whatever he likes . . . I thought it was quite charming."

Marriage, six children and romantic headlines would more than fill most people's lives, but Lady Antonia Fraser of the 20th-century gossip columns coexisted with Antonia Fraser of the 17th century. She began her biographical writing in the mid-'60s, with the story of Mary, Queen of Scots, a tragic young woman who, in the late 16th century, spent half her life in captivity at the whim of Elizabeth I. A woman of great romance, beauty and hope, queen of France and Scotland, she fared ill in both love and life and was executed without fanfare at the age of 45. Antonia Fraser's "Mary, Queen of Scots" won the James Tait Black Prize in 1969. Her career as a historian was well and truly launched.

Not resting on her laurels in matters historical or familial (she produced babies faster than books), Lady Antonia turned to Oliver Cromwell, Puritan leader of the revolutionaries who separated Charles I from both his throne and his head. Her 1973 biography, "Cromwell, the Lord Protector," was followed in 1979 by a life of King Charles II, an exile, statesman, roue' and restorer of the monarchy. Both these massive books demanded enormous amounts of research and both were hailed as triumphs of biography and narrative history.

All this time, however, another idea was cooking, an idea that impinged on all the areas she had previously researched, the idea for "The Weaker Vessel" -- "my most ambitious book." While working on Queen Mary, Cromwell and King Charles, she kept unearthing stories about women in the wings of history. "This is fascinating," she remembers saying to herself. "This story goes down when it should be going up." Despite initial skepticism, her publishers on both sides of the Atlantic encouraged her to go ahead.

"The Weaker Vessel" looks at many different areas of life for 17th-century women: marriage, birth, widowhood, divorce, prostitution, the stage, business and so on. Each chapter is a maze of interconnected life stories of women, almost always pregnant, ending all too often in sudden death, mostly in childbirth. The book's organization is a tour de force. "It was very, very difficult," she recalls. "When I started to write, I remember saying to Harold, 'I'm writing about 51 percent of the population over 100 years, trying for a strong narrative flow, anecdotes and characters. I'm in despair. I may throw the whole thing in the wastepaper basket.' " She persevered, writing in fact for 15 straight months to complete the manuscript.

The stories of these women are fragmentary and deeply affecting. The book begins with marriage and the pathetic tale of 14-year-old Frances Coke, later Lady Purbeck, who was "tied to the bedposts and whipped" to force her to agree to marry 26-year-old Sir John Villiers, a charmer who "suffered from periodic fits of insanity of a manic nature which might lead him to smash glass and 'bloody' himself." But her youth and his illness were no deterrent to their relatives, who could think only of her money and his title. The pair were duly married with much festivity in the presence of King James. They did not, Lady Antonia points out, live happily ever after.

She is asked for her favorites among the book's huge cast of women and children. "Depending on my mood, I say either Catherine Sedley or Mrs. Cellier." The former was a skinny, plain but witty and determined woman who became the mistress of Charles II's brother, the Duke of York: "I felt I had to include a royal mistress, and I'd done Nell Gwynn one of Charles' ." Fortunately, there was no lack of Stuart courtesans to choose from, and the lively Catherine bore James children, stored up a healthy fortune for herself, and evaded the thrall of marriage until she was in her 40s. Mrs. Elizabeth Cellier, a midwife, fared less well. For although she was an outspoken credit to her profession -- a vital one to the constantly pregnant women of the time -- she became enmeshed in various plots against the king and got herself tried for high treason and thrown in the stocks.

It was not only her love of the 17th century that drew Lady Antonia to the subject of "The Weaker Vessel." Her own experiences were crucial: "Having children of my own was a great asset. It enables me to say, I hope not presumptuously, that only someone like me could have written this book. A young man with a PhD, however sympathetic, couldn't understand. I think it's very important to bring home to people that if you are writing about women there is this difference, which isn't just a biological joke. I was pleased that a number of men have said to me that they never really realized what women went through in those times until they read the book."

Why, then, did several critics go out of their way to praise the book for not being a feminist tract? "I didn't want to write a tract," protests Lady Antonia, "but I think it's a profoundly feminist book myself." She laughs -- "unless I've missed something."

The book has a clear thesis: that women gain ground in times of crisis, especially in times of war (as in the English Civil War), and then lose it again with the return of peace and prosperity. The position of women in England clearly declined in every area -- except perhaps sexual freedom -- after the Restoration of Charles II. Could that happen now? Could the ground gained by women since the first and second world wars be lost again? Although she finds it hard to imagine such backsliding, Lady Antonia takes a long view of history and points out regretfully that the daughters of women, from Iran for instance, who were at Oxford with her 30 years ago, are now banned from any kind of university education. It's much too soon, it seems, to take equality for granted.

On a less cosmic note, one wonders if it is easier to work now that all her children are grown. "It ought to be," she answers slowly. "What one forgets, when you think it'll all be better when the children are grown up, is that the real problems in writing aren't actually anything to do with six children and chickenpox. When you're coping, you think when they don't have chickenpox I'll be able to write fluently and easily. Alas! Not true! The problems remain the same: depression, exhaustion, wondering if you're on the right track."

In fact, she's not at all sure that the pressures of trying to do it all are not in some subtle way helpful: "When I wrote 'Mary, Queen of Scots' and 'Cromwell,' I was so short of time that when I did get rid of the children to prams or school, I wrote like a bat out of hell. Perhaps some of the narrative excitement that people have liked in those books was the result."

Those babies in their carriages are now grown men and women. Grandchildren? "I'm afraid not. These girls keep writing books instead of having babies." But what can one expect when they are heirs to the tradition of a family known in England as the "Literary Longfords," after Lady Antonia's parents, the Earl and Countess of Longford.

Lady Antonia's eldest daughter, Rebecca Fraser, is working on what her mother calls "a feminist study of the Bronte s"; her second daughter, Flora Powell-Jones, has published a novel, done research for "The Weaker Vessel" and is now writing a biography of Lady Hamilton, Admiral Nelson's mistress. Their grandmother, Lady Elizabeth Longford, the biographer of Queen Victoria and the Duke of Wellington, is at work on her memoirs; their grandfather, Lord Longford (known affectionately in England as "Lord Porn" for his crusade against pornography), has just completed a memoir about the 11 British prime ministers he has known personally, "Eleven at Number Ten."

And there's more: Lady Antonia's brother Thomas Pakenham, author of a definitive history of the Boer War, is working on a massive history of imperialism, while sister Rachel Billington has just published her fifth novel. Poetry is not neglected on the family bookshelf, as another sister, Judith Kazantis, is a feminist poet with a new volume just published in London by Virago Press. Lady Antonia may get "fed up" with talking about her family (and says they get equally fed up talking about her), but reciting even the bare list of their publications compels astonishment and inevitable curiosity.

Lady Antonia's contribution to the family legend doesn't stop at major historical biographies and studies. She is also the author of four mysteries (with a fifth on the way), featuring a cool, single, liberated amateur sleuth called Jemima Shore. Her supersleuth has already starred in a television mystery series.

Future plans for the lady who has done it all?

"I don't know what historical work I'll do next, but I'm as sure as I can be of anything that it will be within the bounds of the 17th century. I feel I'm beginning to understand those people more than people around me in my own time. I know about their relationships to each other. Really, the more you find out about the 17th century the more interesting it is. I'm at home there."