Bette Davis' daughter is bracing herself.

Some people won't like B.D. Hyman's depiction -- in her memoir "My Mother's Keeper," which will debut on national best-seller lists Sunday -- of Davis as a foul-mouthed, neurotic, bullying drunk. The public reaction could be even more hostile in Los Angeles, where Hyman is headed for the next leg of her media blitz and where some Hollywood types are making prepublication noises of disbelief and contempt.

"It depends," says Hyman, calmly finishing her room-service BLT, "on whether they know Mother or not. If they do, they're terribly sympathetic.

"With someone as famous as my mother, people feel very protective," Hyman acknowledges, arranging herself on a sofa in a small sitting room at The Plaza. "Such a person has a different standard than we mere mortals. I don't happen to believe that. Mother abuses everyone she comes in contact with -- her family, her employes, business people, other actors and actresses."

Hyman, 38, says she wasn't anxious to leave her two sons at home in Freeport, the Bahamas, with her husband Jeremy for this whistle-stop trip. For a month, she says, she wasn't sure she even wanted to publish the book it had taken her 18 months to write. She's given away much of the $100,000 advance to her church, the Assemblies of God Calvary Temple in Freeport, to evangelist Pat Robertson's 700 Club, and to "various Christian programs all over the world." And she's determined that "My Mother's Keeper" (unlike "Mommie Dearest," Christina Crawford's posthumous revenge on her movie-star mother), will never become a movie. Hyman's motives, she insists, are noncommercial. "I wrote this truly as an open letter to my mother."

Hyman's mother, according to the book, threatened, taunted and tyrannized B.D. (for Barbara Davis) and her adopted brother and sister, failed to protect them (or herself) from her violent fourth husband, Gary Merrill, staged mock suicides, and sank deeper into alcoholism as her career declined. She pushed her daughter into precocious affairs, then tried to sabotage her marriage (" . . . if I wanted to I could take him away from you right now," she remembers Davis saying), eventually turning her attacks, primarily verbal, on her grandsons. It was at that point two years ago, Hyman said, that she could no longer juggle the conflicts.

"My little boy Justin would cry and plead with me not to let my mother come visit. 'Mommy, she hates us, she hates us.' " Hyman's voice catches for the first and only time; she is otherwise perfectly composed. "A little child doesn't deserve this, however brilliant the other person is, however much fame she attains.

"Her vicious attitude was affecting all of us. Every holiday came this dread that this woman was going to come in and terrorize my sons. There was such pervasive nastiness that it was no longer fair of me to subject my husband and children to it. Holidays are a time of love and joy -- and suddenly I realized my little boy would have an entire childhood of dreading Christmas. And whose fault was that? The fault was mine. Was I going to be my mother's daughter or my children's mother?" she says. "I'd thought I could be both; I no longer could.

"My choice," Hyman says, "was to eliminate my mother entirely from my life or try, in this rather unusual route, to reach her." Davis has not seen her grandsons since the spring of 1983 when, according to Hyman, Davis threatened 6-year-old Justin with a spanking if he didn't eat his peaches, and told his mother that too much coddling would make him "a sissy." Although they correspond, Davis has not spoken with her daughter since December, when Davis learned that the book was forthcoming.

Hyman did send Davis a Mother's Day card before embarking on her tour, however. "I'd like very much to have a relationship with my mother, if she can accept me the way I am, accept my family the way they are," Hyman says, formally. "But Mother believes love and ownership are synonymous. She thinks possessive love is the only kind, which I find very sad."

Whether it's her recent religious awakening ("It's given me tremendous strength and belief in what I'm doing"), her years of media experience, or something else providing her tranquility, Hyman exudes cool poise. She's got Bette Davis eyes and some of her vowels, too -- it's eyther, and rawther. But the quiet demeanor isn't reminiscent of any Bette Davis role: Hyman sits with hands in lap, feet crossed at the ankle, voice pitched low. She doesn't flinch when she describes Davis' drinking, screaming or lying, and she doesn't apologize.

Was there no other way to persuade Davis to change her behavior than by putting her plea between covers? Wouldn't an interview have accomplished as much? "The reaction would have been the same; she'd have had the same rage, the same conviction that it was lies," Hyman says, shaking her head. "And in a book I could give a complete portrait. I certainly didn't want to vilify her, and I don't think I did."

What about the "60 Minutes" segment purportedly showing Hyman in an about-face since a 1979 interview that contained no hint of her troubled childhood? "I'd only told part of the truth and stayed neutral," Hyman says of the earlier tape. "There was no serious conflict I couldn't handle between my children and my mother then."

Did it occur to her that Morrow had also published "Mommie Dearest"? No, Hyman says. "It's also Pat Robertson's publisher," she adds. Hyman is a 700 Club member, pleased at the prospect of appearing on his show during the tour.

So far there is no indication that her mother is accepting her revelations in the loving spirit Hyman says she intended. "Because Mother lives in a fantasy world. She'll look straight in my eyes and say, 'Your stepfather never laid a hand on you.' And my stepfather Gary comes right out in People magazine and says sure, they drank a lot and knocked each other around."

And what if, aside from $100,000 plus royalties, "My Mother's Keeper" doesn't ultimately succeed? If Bette Davis (fully recovered from her strokes, Hyman says, and staying with a friend in Connecticut) doesn't curb her tongue and her temper and learn to be a proper grandmother? "I don't think I will ever stop believing it could happen," Hyman replies. "I don't have a time limit on it."

"My Mother's Keeper" has already paid one dividend, though, Hyman offers. Her father, artist William Sherry, got short shrift in Hyman's book and little attention in her life. Davis had always said he'd run off with the nanny when B.D. was 3 "with never a backward glance. So I never developed any positive emotions about my father. He had nothing to do with me."

Hyman and her father merely exchanged Christmas cards, and one time paintings, until last week he wrote to his daugther saying he was proud of her and revealed his side of the story. The truth, says Hyman, who believes Sherry, was that Davis saw Gary Merrill in a movie, "thought he was the sexiest thing since ice cream, and threw Dad out of the house." Sherry didn't get to know Marion, the nanny to whom he is still married, until she began bringing B.D. to him during the year he had visitation rights.

"He said I became so ill and overwrought after I came home from visiting him, breaking out in hives and crying for hours, that he felt he was selfish, doing me irreparable harm, and if he loved me he'd let me go," Hyman discloses, looking pleased. "He's kept his peace for 33 years; I don't think he'd ever have spoken out if I hadn't written a book. Now, all of a sudden, I'm going to get to know my father. He's going to visit us in Freeport; my boys will have a granddad."

The life the Hymans live there sounds peaceful; they go boating and diving and all attend church. B.D.'s paintings will be shown in a Freeport gallery. Jeremy Hyman, who married B.D. when she was 16, trades commodities and has other business interests his wife is vague about. They are beginning another book, "A Sequel, Our Christian Testimony and the Continuation of Our Lives."

Several evenings a week, the elder Hymans design and build sets for the Freeport Players Guild, an amateur theater troupe. Her older son, Ashley, 16, who had a part in one of his grandmother's television movies, has "a real flair for acting," Hyman says proudly.

And B.D. herself? She had a bit part as the girl next door to Davis and Crawford in "What Ever Happened to Baby Jane?"

"Oh, no," Hyman says in alarm. "We're with the production crew. It would take an awfully good reason for me to be on a stage."