JANE AUSTEN's biographers will never succeed in winning her favor if they keep picking on her sister. Scholars do not always care to court their subjects' assumed approval, of course. But it is a truth universally acknowledged that every single one of Jane Austen's admirers fondly imagines enjoying her confidential friendship, for the delight of snickering together at the foibles of all those other, impossible people.

None of us ever conceives the possibility that the exquisite laughter might go in the other direction.

Few authors are so "would-haved": Miss Austen would have relished this; Jane wo have been vastly amused at the ridiculousness of that. Yet it is safe to say, from evidence in her letters, that she would not have cared for anyone who attacked her real life- long confidant, best friend and roommate, her elder sister, Cassandra Austen.

They can't seem to help themselves. John Halperin and George Holbert Tucker, like a long line of their predecessors, voice the selfish wish that the sisters had been more often separated in life, in spite of their heroine's specific statement that she could not bear being long deprived of her dearest companion.

If they had lived more apart, you see, Jane Austen would have written more letters. The full fury of the future groupies is concentrated on Cassandra Austen's anguished bereavement, when she selectively burned letters.

Those letters that were written and spared in spite of her sister are the chief sustenance of Jane Austen's biographers. That is all there is, aside from some family memoirs written from a distance of time, and whatever can be extracted from the fiction and made to match probable events in her life.

Nothing new ever seems to surface. Not even an overlooked postal card from Bath. No unknown diaries have appeared to flesh out the skimpy details of her life, or supply a scandal to make up for such an unfortunate dearth of juicy gossip. We loyalists would dearly love to find that there was, after all, a passionate romance in the life of one we consider so superlatively desirable. Even a few new details about the paltry romances she did have would do. But none of these is forthcoming.

One can understand, then, why the biographers churlishly chastise Cassandra for not hiding herself, so that her sister would be forced to communicate in writing, and attack her for the high crime of destroying letters.

However, Cassandra was, of all people in the world, then and now, the best-qualified to "would-have" Jane Austen. We don't even know that her act of literary vandalism was not committed on the express deathbed wish of our idol, who had a documented distaste for the kind of celebritizing her modern fans would like to do. Nobody else will ever be devoted enough to respect that wish of hers. (Are there any among us who would have refused, as she did, to go to a party for the purpose of meeting Madame de Stael?)

In any case, the result is that Jane Austen biographers have a problem. There simply is not that much known about her, and what is known indicates a bustling, happy and insulated family, a flirtatious nature that never found its worthy match, and a literary dedication that sought satisfaction in the work itself, the praise of a few, and financial remuneration, but certainly not in personal publicity.

THERE IS, therefore, a lack of freshness and drama in the material. Tucker's solution was to go farther afield and write about the wider family circle. Halperin's was to take what is known and reerpret it, so that what was accepted as happiness and humor is presented as jealous rivalry and bitter cynicism born of frustration.

Tucker's family history is certainly the more entertaining book. If Jane Austen's life was lacking in incident, she had relatives who had it in abundance.

There is cousin Eliza, probably the illegitimate daughter of Warren Hastings (the governor-general of India prosecuted for corruption and cruelty by Edmund Burke), who married a French count, lost him to the guillotine, and swept into the Austen rectory as a sophisticated older woman to bewitch the young Austen brothers, one of whom she finally married.

There is Aunt Jane Leigh Perrot, the prototype of the rich, childless relative of uncertain temper on whom so many family hopes are pinned. She was the victim of a scam by some Bath lace dealers and spent a winter season in jail before she was acquitted, her devoted husband living voluntarily at her side and arranging to accompany her into the disgrace of exile if necessary.

And there were handsome papa; zany mamma; brother Francis who became admiral of the fleet; brother James, who worked an account of the running of the bulls at Pamplona into a prologue for "The Tragedy of Tom Thumb"; ne'er-do-well brother Henry, who passed his Greek examination only because it consisted of questions in English about his connections; and favorite niece Fanny who, as the grown-up Lady Knatchbull, described her aunts Jane and Cassandra as being slightly common, unrefined, and saved only by association with her branch of the family from being "very much below par as to good Society and its ways."

When Halperin describes this family, it is all ominous, rather than funny. For example, he makes Mrs. Leigh Perrot's written conclusion after her ordeal, the discovery that "Lace is not necessary to my happiness," into merely a sober resolution to give up the wearing of lace.

In the immediate family, the sisters' clseness becomes a form of sibling rivalry, impatience with the hijinks of small nieces and nephews becomes an antipathy to children, exasperation with the mother's hypochondria becomes a lifelong alienation, and even humorous commentary on strangers, a sign of meanness.

Jokes about the deaths of the duke of Gloucester, the duke of Mecklenburg-Strelitz and the marquess of Granby are condemned as coldblooded and unsympathetic -- as if one would expect Jane Austen to go in for hypocritical mourning for titled strangers!

AND HER use of marriage as a plot device is seen as the preoccupation of an embittered spinster, as if satisfactorily matched writers never ended their stories with a wedding. Discussions of money and marriage are analyzed with an apparent innocence of the fact that what a couple was going to live on was once considered as important a condition to marriage as, say, sexual compatibility would be today. One also suspects the biographer of unfamiliarity with the forms that teasing kes in an affectionate family of a satirical turn.

Anticipating dislike of his debunking, Halperin warns, "With those who think the great should never be criticized, I simply cannot agree." Actually, it would be hard for even the strongest loyalist to disagree with that premise. Rather than argue, we will have to content ourselves with imagining how the two Miss Austens, alone in their room, might satirize someone who believes that apparent happiness must be a cover-up, that family hatreds are inevitable, and that being funny about life is a sign of misery.

Perhaps that also would have been the occasion for deciding not to let people of that kind get ahold of the more intimate family mail.