NEW YORK - When most of us think of Jacqueline Kennedy Onassis, we think back to the perfectly coifed first lady of the early '60s in a stylish shift, a string of pearls, a pill box hat. Or the Jackie O of the next decade, the rich widow in huge sunglasses that shielded her from the world.

We probably don't think of a middle-aged working woman making her own photocopies, waiting on line to speak to the boss, or sitting cross-legged on the floor, arranging photos and puffing on cigarettes.

Yet this was Jackie's third act - the Jackie who joined the work force in her mid-40s and spent nearly two decades as a book editor. By all accounts, it was one of the most satisfying periods of her life.

"She didn't do this just to have a job," says Bruce Tracy, a former colleague at the Doubleday publishing house. "She loved this. This is what she was passionate about."

Suddenly, in a span of just a month, two new books are examining this little-known part of Jackie's life, giving readers a new slant on a woman who has fascinated Americans like no other in our history.

"People think about Jackie's clothes, about her marriages, maybe her redecorating the White House," says historian William Kuhn, author of "Reading Jackie: Her Autobiography in Books," released this month. "But her editorial career was longer than her two marriages combined. It says more about who she was as a person, because this is something she actually chose to do."

Of course, she didn't need the work. Kuhn notes how women of Jackie's generation were taught to be great wives and great mothers, making it all the more striking that she would choose to learn a new career so relatively late in life. "It speaks to a kind of quiet feminism that she and other women of her generation had," he says.

Jackie was 46 when she was hired by Thomas Guinzburg at Viking Press, not long after the 1975 death of Aristotle Onassis. Clearly Viking wanted her for her name. And her early efforts - she spent only two years there, before moving to Doubleday - were a learning process. But her productivity skyrocketed as the years went on. "Yes, some of this was handed to Jackie," says Kuhn, whose book is being published by Doubleday itself. "But the fact is, she amassed a list of books that publishing professionals are in awe of today."

That list includes books on everything from art to European and American history to photography to fashion to religion. It includes children's books by Carly Simon, and Michael Jackson's autobiography, "Moonwalk." She worked on a trilogy by the Egyptian writer Naguib Mahfouz, several books by Bill Moyers, and a series of Tiffany style books.

And then there was her well-documented love of dance, particularly ballet, which led to the best-seller "Dancing on My Grave," by ballerina Gelsey Kirkland and her husband, author Greg Lawrence. Working with her on the book, an account of Kirkland's descent into drug addiction, was "a humbling experience," says Lawrence, who next month comes out with "Jackie as Editor: The Literary Life of Jacqueline Kennedy Onassis" (Thomas Dunne Books/St. Martin's Press).

Lawrence recalls how at an introductory lunch with the couple, Jackie burst into tears at their story, saying, "I want to do this book!"

"Jackie fought for us," says Lawrence. "That's what I really admired about her. She had to fight for her books. And when we ran out of money, she would call us and say, 'I got you more, just don't tell anyone.'" Later, she persuaded the couple that the book should be 300 pages rather than the 600 they were writing. "That voice, it would just completely disarm you," he says.

There were perks to being Jackie O - she worked only part-time in her office and spent a lot of time working at her Park Avenue apartment, where she would sit in her library with authors surrounded by her books, smoking out of a long, ivory cigarette holder, Kuhn says - not to mention taking the summer on Martha's Vineyard.

But it was striking to many how quickly she shed the trappings of celebrity, munching on sandwiches at her desk, waiting nervously in corridors for face time with the boss, always coming to the reception area to meet her visitors and making her own calls.

"She never said 'Get me so-and-so on the phone,'" says Tracy, the former Doubleday colleague, now a freelance editor, who assisted her on a number of books.

She died on May 19. The next day, her son, John Kennedy Jr., told the assembled media that his mother had died "surrounded by her friends and her family and her books and the people and the things she loved."