BOOK REVIEW : A Gritty Story of Assimilation : BONE By Fae Myenne Ng ; Hyperion; $19.95; 224 pages

In each national variation on the American novel of ethnic assimilation and estrangement, there is the battering of the old country by the new, the pains and gains of the young and the cleavages and dilutions in the family traditions. In none of them does the family loom so large as in the work of Chinese-American writers.

More than with Irish-American, Italian-American or Jewish-American stories, the emphasis is on what is lost or sacrificed. In different ways and to different degrees, we find in the fiction of Amy Tan, Gish Jen and David Wong Louie something much graver than simply a wry, a difficult or even painful adjustment.

The edifice of tradition is more complex and redoubtable, and it collapses in dangerous shards. What goes on inside the Chinese-American protagonists can approach a deranging displacement. Most distinctively, the displacement is registered not just in the old but in the young as well.

Fae Myenne Ng’s “Bone” is in this tradition. Its story of an old San Francisco couple and their three grown children gives a sense of the wildness underlying the changes that the two generations go through. Tragic things happen, although the book is not a tragedy, nor is it written in tragic tones. The voices of the narrator--oldest of the three children--and of the others are terse and percussive. They shift abruptly from the emotional to the matter-of-fact with an effect that is sometimes comic and often coolly illuminating.

Leila tells her family’s story. Mah and Leon, her mother and stepfather, are immigrants who have struggled all their lives to survive. Mah sewed long hours in a Chinese sweatshop and, after hours, at home; more recently, she opened a modest Chinatown clothes shop.

Leon shipped out for months at a time as a merchant seaman; in between, he took a variety of grueling shore jobs. Leila is a social worker in the Chinese community; Nina, the youngest, lives in New York and works as a tour guide for American groups visiting China. The middle sister, Ona, kills herself by jumping from the upper floor of a San Francisco housing development.

Ona’s death is the shattering of the family vessel. Leila’s account portrays the pressures that led to it and the secondary explosions that followed. She tells it as a series of vignettes that range back and forth between past and present.

Ona is not really the focus. We learn relatively little about her or, for that matter, about her death. As a child she was Leon’s pet. Later he threw her out for going around with the son of a business partner who had swindled him. She was, in that sense, a rebel against her family’s ways and means.

But what we gradually see, in Ng’s lively and artful unfolding of the story, is that they all were. Nina has kept her distance, although she stays in touch and returns for Ona’s funeral. Leila has stayed in San Francisco to mediate between Mah and Leon, who are stormily apart as much as stormily together. But she lives with her kind, handsome and--ethnically speaking--liberated Chinese-American boyfriend, an auto mechanic. Both sisters feel insufficient.

“She thought I had the peace of heart, knowing I’d done my share for Mah and Leon,” Leila says of Nina. “And I thought she had the courage of heart, doing what she wanted.”

Solicitous and impatient, guilty and pluckily inquisitive by turns, Leila reveals herself as well as her story. Nina, more distant, is drawn with less detail and equal sharpness. “I know about should. I know about have to, “ she replies when Leila refers to their parents’ emotional neediness. “We want to do more, we want to do everything. But I’ve learned this: I can’t.”

The book’s strength and surprise, however, lie in its portraits of Mah and Leon. For a while, these are amusingly colorful characters, warring with each other and with America. Mah seems to be the traditional Chinese matriarch: bossy, emotional and continually deserted by Leon. He goes to sea or flees periodically to a downtown hostel, littering his room with half-finished repair projects and mooching around with his old Chinatown cronies.

Amid this agreeable picturesqueness and a lively Chinatown scene, Ng inserts a deeper story. It is Mah and Leon, in fact, who are the real rebels. Immigrating to America was a leap into peril; it meant two lifetimes of punishing labor and social humiliation. It meant settling for the “bone” of the title. It meant that their children could live with more choices--and with burdens of guilt and cultural confusion.

But Mah and Leon are rebels against their own choices as well. Leon’s flights are part of it. So was Mah’s affair with her sweatshop boss. So was her unexpected agreement to go on a Hong Kong vacation with Nina shortly after Ona’s death, while Leon, the apparent freebooter, stays home to take care of things.

“Bone,” although it can be facile and sentimental--Leila’s boyfriend is too much of a perfect prince, for example--tells a gritty and moving story. Inside their cantankerousness and traditionalism, the two old people are as impulsive and unconstrained as children, free spirits in their yokes.