TODAY IS HER birthday, and it offers an alibi -- any will serve -- to talk about Jane Austen and her mystery. Why does this novelist, who was born 209 years ago, and who wrote about the English gentry on, as she said, "two inches of ivory," continue to hold readers in thrall?

I can tell you that one account of a Jane Austen Society meeting brought more mail than any other topic discussed in this space.

The Jane Austen cult was the subject of a recent front-page story in The Wall Street Journal. Five hundred and sixty thousand copies of her novels have been printed since 198l. This might well amuse the daughter of the rector of Steventon, who offered her first novel, "Sense and Sensibility," to a publisher with such diffidence that a refusal came back by return of post.

She had a few contemporary admirers. The prince regent of England, for instance, kept a complete set of her novels at all his estates. He never knew when he would require a quick fix of wit or principle. Today, my friend Linda Wertheimer has three sets of Jane Austen, one bound in leather, a second, more pedestrian hardback and a third in pocket books, of a size suitable for being slipped under a notebook at a press conference dealing with say, "revenue- enhancement" or possibly the choice of a new Democratic Party chairman.

Sir Walter Scott was smitten by her. So is Nora Ephron, an utterly contemporary young woman, who reads "Pride and Prejudice" at least once a year, because she is entranced, as any sensible person would be, by Elizabeth Bennett.

Volumes have been written about Jane Austen since she succumbed to an unknown illness in 1817 at the age of 41. I have gone through some of them, enjoying them most when she is quoted. Her critics point out that she dodged the hurly-burly of life, averting her eyes from passion, never writing about childbirth, death, poverty, war or any of life's more wrenching moments. Louis Kronenberger observes that some people find her "tea-tablish." Charlotte Bronte laments the want of the "heaving bosom" in any of her novels.

And yet, new Jane Austen societies are formed every day, and once a year they meet in convention to devote two days to impassioned discussion of one of her six novels. Emma and Anne Elliot and Fanny Price seemed to be in the room.

Maybe it is because she deals with one subject, what is called today, "interpersonal relationships" and the eternal theme of young women in search of husbands. Jane Austen recorded the pursuit with fidelity and clarity that has never been matched. The young woman in the singles bar recognizes the truth, if not the circumstances, of her account.

She also describes loneliness, mostly through her delineations of old maids (she was one herself) who must be ingratiating, obliging, never revealing their own feelings in order to be tolerated. Miss Bates of "Emma" is her masterpiece in this line. Miss Bates is forever praising, doing, offering, hoping to be included. Emma makes fun of her, in one of the most memorable scenes of that much-praised novel, and when Mr. Knightley, her mentor -- and her future husband -- takes her to task, she gives way to bitter tears and turns a corner in her life. The thing about Jane Austen is that she is as decent as she is perceptive.

That's a stab at the "why?" The "how" remains.

She never left the south of England for any length of time, never traveled abroad, never met a writer or even corresponded with one. She had no friends outside her warm family circle, to whom her novels were read aloud with great delight and pride. She had no other sources of encouragement, except the prince regent's librarian, who suggested she write a romance about Saxe-Coburg, and some readers who marveled that she had taken them into another world.

She created those compelling characters and wrote those incomparably fine-grained books on a portable writing desk in the parlor, subject to frequent interruptions from family members, servants, visiting nieces and nephews wanting counsel on courtships and later on novels they were writing. She was warned of their coming by a squeaky door which she forbade to be fixed, and simply thrust the pages out of sight as she rose to greet them.

By today's standard, she had nothing: no word processor, no creative-writing courses, no workshops on the novel, no prospects, if successful, of being sent on publicity tours, autographing parties and appearances on late-night television shows with Joan Rivers.

All she had was her sharp eye, her true pen and her sense of what men and women are -- and what they ought to be.