New York — In 1949 Helene Hanff, then an impoverished young writer with a rich taste for out-of-print literature, wrote a letter to a used-book shop in London. Addressing it to ''Marks & Co., 84, Charing Cross Road,'' she requested a Latin Bible, a book of Hazlitt's essays, and other volumes on a list of her ''most pressing problems.''
Such were the unlikely beginnings of a long and happy friendship-by-mail, a BBC television drama, a Broadway play, and a curiously affecting little book called ''84, Charing Cross Road,'' the collection of letters that made their way between Ms. Hanff's New York apartment and the dusty Dickensian reaches of Marks & Co. for nearly 20 years.
For Helene Hanff the success of ''84, Charing Cross Road,'' first published in 1970 and still available in both hard cover and paperback (Avon Books, 1979), was, she believes, ''the greatest accident of my life.'' It was one that happened after years of reading scripts for $40 a week, baby sitting, writing ''arty murder plots'' for the early ''Adventures of Ellery Queen'' TV series, and, most time-consuming of all, struggling in vain to get her plays produced on Broadway.
Accident or not, it proved consistent with a theory she encountered in the theater called Flanagan's Law. ''Its basic premise is that no matter what happens to you in your career, it's unexpected,'' she says.
Ever since she first came to New York as a stagestruck 19-year-old from Philadelphia determined to conquer Broadway, Ms. Hanff has had good reason to believe in Flanagan's Law. Arriving in town as the winner of a prestigious Theatre Guild fellowship, an honor bestowed on Tennessee Williams and Arthur Miller the year before, she had every reason to believe she would fulfill her goal.
''So, of course, with a great beginning like that,'' Ms. Hanff comments some 40 years later, ''I didn't have a chance.''
Instead, like a lot of other would-be playwrights, she eventually found herself writing scripts for an entertainment upstart called television, then a live medium based in New York. Along with mystery plots set in art galleries and concert halls for ''Ellery Queen,'' she wrote scripts about the lives of historical figures for ''The Hallmark Hall of Fame.'' But just when she seemed well on her way to accepting her lot in this unexpected career, Flanagan's Law intervened. Television moved to Hollywood and changed into a form for which she did not want to write.
''When TV stopped being live, you had to be a screenwriter to know how to write for it,'' she says. ''I wasn't comfortable writing for the camera. And it became impossible to sustain anything that wasn't destroyed by six commercials.''
So then the playwright-turned-scriptwriter became a writer of books. Her first was an autobiography, ''Underfoot in Show Business,'' first published in 1960 and recently reprinted in hard cover by Little, Brown. It is, as she states in the introduction, about life among ''the other 999,'' those Broadway hopefuls who are not the one in a thousand who ''turns out to be Noel Coward.''
Not becoming Noel Coward had its compensations, the often funny, sometimes poignant book reveals. There was friendship with others among the 999, a fine honing of survival skills while living on the edge of poverty, and the ever-present hope that play No. 14 might be the one finally to make it past the rounds of producers and onto the stage.
After ''Underfoot in Show Business,'' Helene Hanff wrote a steady stream of children's books and magazine articles. In the late 1960s she wrote ''Movers and Shakers,'' a book about the young social activists of that decade.
All the while she kept up the correspondence she had begun with the London bookshop in 1949. Most of her letters went to Frank Doel, an employee at Marks & Co. who patiently tracked down her requests for Walton's ''Lives,'' ''a nice English 'Angler,' '' and a Samuel Pepys diary ''for the long winter evenings.''
But acquiring an oddly assorted collection of used, antique, and out-of-print books was the least of what the correspondence yielded. Realizing that England was enduring severe postwar rationing, she sent the shop employees parcels of fresh eggs and other hard-to-get items. Those and her humorous, chatty letters prompted correspondence with other staff members and with Frank Doel's wife, Nora.
As the years passed, she kept in touch with the changes in their lives and they with hers. Despite many invitations to come for a visit, there never seemed to be enough money or the right opportunity to make the trip. When Frank Doel passed on in 1968, she had lost a dear friend whom she had never seen or spoken with.
Needing a respite from her work on ''Movers and Shakers'' and ''too broke to go to the movies,'' she decided to put the letters into some kind of literary form. ''My first thought was to make them into a short story for The New Yorker, but when I finished I had 66 pages, which was far too much,'' she says. ''A friend suggested I include a few more and turn it into a book.''
Although ''84, Charing Cross Road'' received enthusiastic reviews and a small but avid following in this country, the big success came in England, where it was an instant best seller. ''The real Flanagan's Law is that I became famous in the wrong country,'' she says.
Soon there was a BBC production adapted from the book, with Anne Jackson playing the role of Helene Hanff. ''She did such a good imitation of me that my friends insisted my voice had been dubbed in,'' she says. ''But it wasn't. Anne just happens to do Katharine Hepburn and myself very well.''
After the book was published, Ms. Hanff finally got to London, a trip that resulted in a meeting with Nora Doel and in one of the ''two most extraordinary moments in my life.'' This occurred at the site of Marks & Co., which had gone out of business a few years earlier, where she was guest of honor at the dedication of a plaque marking the old storefront as a literary historical landmark.
Two days after the ceremony, ''84, Charing Cross Road,'' adapted to a play by James Rouse-Evans, opened in London's West End for a long and successful run. The Broadway production, which starred Ellen Burstyn, did not do well, closing after three months. (This summer the play is touring the United States with Shelley Winters in the lead.)
The play lasted long enough on Broadway, however, to furnish Ms. Hanff with the other most extraordinary moment in her life. This one occurred during opening night, when her brother sat in the audience next to Rex Harrison. When the actor learned who her brother was, he turned and said, ''You tell your sister that she's the toast of London.''
What made being the toast of London and the impetus behind a literary historical landmark especially sweet is that they both took so long to achieve. ''If someone had told me that I would have to wait 30 years for success and that it would come in such a roundabout way, I'm not sure I would have bothered to try,'' she says. ''And yet I'm glad that it happened this way, that I'm getting it all at the end. You appreciate something so much more when you've been without it.''
Another benefit, Ms. Hanff insists, is that it's actually a lot of fun to look back at the hard years. ''A struggle,'' she says, ''is the greatest thing to live past.''