To turn yourself n a fictional heroine is to reveal a lot, perhaps more than you intend. Linda Fairstein, chief of the sex crimes unit in the District Attorney's office in New York City, has turned to writing crime novels which feature Alex Cooper, a "younger, thinner, blonder version of herself as protagonist.

"There are a few minor differences," says Fairstein. "Alex is very single whereas I've been married for 10 years. But all the professional views are mine expressed through her."

So what do we learn about Fairstein from her fictional incarnation? Four qualities dominate. First, and most important, is her job. In most countries, crimes of sexual assault are prosecuted like other crimes. But in Manhattan back in the early 1970s the DA believed that special skills and sensitivity were required and set up the sex crimes unit. Fairstein became head of that unit in 1976 and is now widely recognised as the foremost US expert on crimes of sexual assault and domestic violence.

Secondly, she has an unambiguous regard for the US justice system. Alex works "on the side of the angels" and her world is neatly divided into good guys and bad guys. Criminals, says her cop friend Mike, are "scumbags" and societal factors like poverty or race never rear their complicating heads.

Thirdly, she is materialistic. The book is full of Calvin Klein clothes, Schlumberger jewellery Chanel perfume, Martha's Vineyard summer houses. One character is dismissed as wearing a suit which was "serviceable for a business meeting but completely lacking in style".

And finally - a minor point but one of interest to this reader - she doesn't think much of journalists. "These are the professionals." says Alex, "who hold a camera in front of a hysterical woman's face and ask how it felt to have watched a grizzly bear eat her three children" Her sidekick cop declares emphatically "There's no such thing as a nice reporter or a thoughtful one."

Designer-suited, spike-heeled and gold-bedecked, the real-life Fairstein looks much as one would expect from spending time with her fictional counterpart, and has the practised answers of a seasoned media handler. A question about her unambiguous attitude to the justice system, for example, brings forth a tribute to her boss and his office: "I am aware that there are occasions when the system doesn't work perfectly but I think our office from DA Bob Morgenthau to the 600 young lawyers who work there, is a model of how the system should work. What I really respect about that office is that we are really encouraged to try to do justice.

A question about the level of violence in America brings on a homage to the Kennedy family. "I can't be here without thinking of losing president Kennedy and Senator Kennedy and losing them to guns and to violence. The violence that family has seen when they contributed so much to our country - I don't understand it and I've worked within and among and around it for over a quarter of a century."

Perhaps because she thinks it will go down well in Ireland, perhaps for personal reasons, (her husband is friendly with Jean Kennedy Smith and they will be spending some time in the Park during her visit), Fairstein's conversation is peppered with references to the Kennedys. JFK was instrumental in her taking the job in the DA's office, she says. "I very much wanted to do public service. I was in high school when President Kennedy was inaugurated and was touched by the famous ask not what your country can do for you, but what you can do for your country. Like many of my peers my interest in public service developed from that."

She intended to spend four or so years there learning the ropes but what kept her there was the great reputation of that office", so that she turned down many offers to go into private practice. "What I like most about the work is being with another human being and helping make things better for her," she says.

So why the move into the solitary realm of fiction? "This is a dream come true for me, writing fiction," she says. " It's very different to prosecuting. I'd like to combine both jobs for as long as possible. I get so much interesting material from the prosecuting job."

This, of course, is the one thing Linda Fairstein has done that Alex Cooper hasn't used those legal cases as fictional fodder. Couldn't that be considered just a little exploitative?

"I am troubled by that," she agrees, "and I've handled a lot of high-profile cases that I've chosen not to write about because they involve real people, real lives that can be identified. I use anecdotal material from cases, I think tastefully, to illustrate different kinds of crimes, but I don't use any that can be identified with particular individuals."

Fairstein is conscious of taking, her place among a burgeoning line-up of female crime-writers. She is a great admirer of Patricia Cornwell's work and deliberately set out to do something similar in her own work. "I am a big fan of Patricia Cornwell, especially that while you're being entertained you're also being given an incredible amount of information." One of the themes of her book is stalking, which has become a big problem in the States, "so I try to take the reader through how an investigation of this type would be conducted and what the different problems are with stalking cases.

With such topical, made-for-celluloid material it is no surprise to hear that "Hollywood is nibbling". However, Fairstein is not in any hurry to sign a contract. "I would be lying if I said not ever," she concedes, "but my literary agent believes firmly in not selling the first book of a series. The experience of Sara Paretsky whose heroine V.I. Warshawski was depicted by Kathleen Turner in the mid-1980s was salutory. "The movie was a disaster and the books never sold as well afterwards," says Fairstein.

"Sue Grafton (another of the US's high-earning murder-mystery writers) has thumbed her nose at Hollywood," she continues "preferring to keep her character Kinsey Mahone a fictional character in people's minds. I'm not ready to thumb my nose but I'd love to get the series established first and then do it."

Surprisingly, Fairstein has no ideas about why so many women writers are currently attracted to the crime genre. Neither, even more surprisingly, does she have theories about why sex crime is so increasingly prevalent in Western cultures. She was fascinated, she, says, on reading the Irish newspapers on the flight over to find so many cases of sexual assault, rape and child molestation. "I don't like to say I could set up business over here" she says wryly,"but..."

Fairstein says one of her "missions" is to change people's attitudes and perceptions to such crimes, particularly any notion that rape victims make poor witnesses. In one high-profile trial she dismissed defence doubts about whether a victim could really identify her attacker by insisting: "The question is not whether she can remember his face but whether she will ever be able to forget it."

The fact that rape is a contact crime means that many victims can identify scars, birthmarks, tattoos and other incriminatory-evidence. "The easiest case I ever had, the man had a scorpion tatooed on his penis," she says. "That's not the kind of evidence you get with someone who held up a bank."

It's difficult not to feel, however, that Fairstein's immersion in the system denies her the objectivity which would have given her book a real edge. Because, although things have improved, 20 years later the legal system still fails the vast majority of sex-crime victims.

Final Jeopardy could have been an insider's insight into a fascinating, complex area. Instead, Fairstein has opted for a bestselling formula. The prose is pure American - people are "brought up to speed" on information, "hang tough" when life gets difficult and "ride it out" until things improve - and so are the values.

For Fairstein is a believer in the American Dream. For her, "America is a great place to live" where "there really is an extraordinary amount of opportunity". And, of course, she's right. Only in America could the opportunity to turn the day job into a winning fictional formula have knocked quite so loud. On the final page of Final Jeopardy one of the characters tells Alex Cooper that she isn't gonna be outta work in the foreseeable future". Ditto Linda Fairstein.