RACHEL BILLINGTON'S NOVEL has, if not much by way of story, a resolute theme hinted at by the title: women (mostly upper-class, Roman Catholic English-women, that is) and their changing lot over the better part of the century. The canvas is as wide in time and narrow in social scope as that of A Dance to the Music of Time (Anthony Powell is her uncle by marriage) and almost as densely peopled with names that come and go over the decades, though personalities to back them up are insubsantial. (Indeed, as they keep popping up, one feels uneasily like a rather deaf guest at a reception, struggling to cover his confusion).

Being a woman is a problem that shifts its focus just a little with each generation, without ever going away. And while being a woman at the top of the ladder entails the same problems, the heady differences between people who can duck off to another well-staffedhouse when life turns vexatious at home, and those who must stick it out among leaky faucets and recriminations are a good part of what makes A Woman's Age entertaining, despite its length and dogged ambition to have more meaning than it can afford.

The action begins at a big country house in 1910 when Violet Hesketh is about five years old, it's she who tells her own story most of the way. Her mother is Lady Eleanor, black-sheep daughter of a duke, who grizzles, "If only I had something to do, I wouldn't be so bored!" What she does is run off to an island she owns off the Irish coast, Eureka, with a young admirer, Nettles. Abandoned to her dim father, who dies in World War I, Violet is later transferred to her scatty mother's care. After a few years running wild on the island, and a few more at a girls' school, she is launched in London society by Lady Eleanor, whose freedom from convention has its limits. "I'm not sure we mean the same society," falters Violet as the project is launched. "Mothers always mean the same society, dear. The one that will bring happiness to their daughters."

Later, at Oxford, Violet, having discovered English lit., sex and love, marries the first member of the middle class she has ever passed the time of day with. The mistake is soon mended and, free again, she flutters through a world of artists, writers, publishers, politicians and priests, but finds true love closer to home: he is her mother's discarded lover, Nettles.

Blissfully married to him, Violet devotes herself to the joys of procreation and lactation, but this pastoral phase ends in 1940 -- she walks out on her family to do volunteer war work in London. When poor Nettles visits her there, he is killed by a bomb, she later learns he was dying of cancer anyway. Midway through life, faced with the choice of returning to her children or taking up a new life in politics, she opts for the unknown.

The rest of the story is told by another Violet, her daughter, through whose eyes big Violet, peremptory, irritable and important, is hardly recognizable as the pre-war fibbertigibbet. Little Violet watches her mother make a speech: "She was confident, strong-voiced, even strident . . . stripped clean of the womanly preoccupations that had held her back. Her energies, which were at their peak, were aimed toward a career" -- a meteoric one. She is elected to parliament as a Labour member in 1945 and quickly enters the party's inner councils as a cabinet minister (along the way converting to Catholicism -- yet another of her unaccountable switches), while little Violet grows up, marries sensibly, produces a daughter, and slides effortlessly into a spectacular career of her own as a writer. Big Violet, having won all the prizes political life has to offer (save that finally copped by Mrs. Thatcher), has nowhere to go but the House of Lords, and when finally, laden with honors and years, she dies during a fact-finding mission to India, it is a death as casual as that of Forster's Mrs. Moore. At the other side of the world, on Eureka, her granddaughter is delivered of an illegitimate baby boy. So closes this cycle of women.

If the two Violets' victorious careers in politics and book-writing seem arbitrary at best, it's not because Rachel Billington hasn't had real-life models to draw from in her own family, whose political and literary fame is legendary (Lord Longford, Elizabeth Longford, Lady Antonia Frazer, etc.). Yet facts are not truth, and in the pages of this fiction they lie inert. Luckily, besides the mass of data, there are homely spurts of real life too, and not serious pretense that human nature can be much altered.

The elder Violet's contemporary, Araminta, whose faithless husband visits her just often enough to keep her pregnant, has allowed her treasured little artistics talents to be engulfed by mothering. When young Violet suggests that if Araminta had been born 30 years later she might have had her career unhindered, Violet, the cabinet minister, replies, "No . . . Women have to want success very much or biology takes over." Her daughter's having it both ways -- career and family -- can be written off to sheer good luck in the man she married.

For the trouble is not only the drag of biology, but the thinly disguised, ages-old masculine conviction that women are at bottom stupid -- and the author keep a keen ear tuned to the dialogue of conflict between the sexes. As Violet tries to have a serious discussion with a suitor, conversation degenerates into a quarrel that lurches from one smarting irrelevancy to the next. Why can't women be like men? he asks. We're as men want us to be, she rejoins: "Be a good wife, be a good mother. Ugh!" "You don't want that. And you don't want anything else either. Women are stupid." And so on, until they end up clobbering each other with the name of Ramsay MacDonald, which for all it has to do with what they are at odds about might as well be Hitler or Shirley Temple.

The frissons of being a bright young thing in the 1920s, the narcotic pleasures of moterhood, the comfort of a loving marriage -- as well as the gnawing anxiety of wondering whom he's sleeping with now, and the guilty high of having an affair of one's own behind the husband's back, are conveyed with true understanding, where Violet's political life is not. The switch from one narrator to another at the moment she turns her back on home to become an M.P. is a way out of the impossibility of making her volte-face plausible. Seen through her daughter's eyes she is a possible woman politician, but not the real Violet.

The passage of the 20th century is marked off with laborious historical references and authenticating period details, sometimes faulty (she imagines, for instance, that in the 1920s Bloomingdale's was an emporium of chic instead of a resource for maids' uniforms and pillow ticks, and uses the world "holocaust" in 1914 to describe war). A more serious flaw is the want of dynamic interaction between the characters that would bring them to a sustained life they enjoy only fitfully as they cross Violet's trajectory. A thin, shrewd novel is struggling to escape from a fat, didactic one.