A WINTER'S CHILD. By Brenda Jagger. Morrow. 468 pp. $17.95.

WORLD WAR I is over, the boys are coming home and the small English town of Faxby is prepared to resume a normal life -- normal in the sense that the gentry will once again be able to have an adequate number of servants, to throw lavish garden parties and to find suitable young men for their daughters. Faxby, in short, is ready to put aside its mourning and return to those easy- to-understand pre-war days.

But the clock cannot be turned back and a new era has begun. Women are bobbing their hair, smoking cigarettes and baring their knees. Housemaids who went to work in munitions factories don't want to return to "service," and former butlers have become ambitious entrepreneurs. The flower of the aristocracy, the young men who left for war with idealism in their hearts, return as emotional or physical cripples, shell-shocked and cynical. Nothing will ever be the same again and nowhere is this more apparent than in the lives of Faxby's wealthiest family, the Swanfields.

Author Jagger skillfully weaves together the strands of many stories to form a fascinating tapestry of grand emotions: of love and lust, of anger and revenge, of jealousy and greed. There is the story of Claire Swanfield, a war widow returning from the front as a nurse, who defies convention and falls in love with her brother-in-law, Benedict. There is Nola, Benedict's wife, an adulteress whose promiscuity leads her into tragedy. And there is 19-year-old Polly, who believes her youth has been wasted during the war and seeks gaiety with all the desperation of a Fitzgerald heroine.

A Winter's Child is that rare book which delivers more than its publicity promises. Its plot has as many twists and turns as a labryinth, and it is written in a graceful style and with great authenticity of place and character. I, for one, simply couldn't put it down. It's one of the best popular novels to come down the pike in a long, long time. PLAYING THE JACK. By Mary Brown. Simon and Schuster. 584 pp. $16.95.

THE year is 1785. The place is any hamlet in Britain. The characters are the members of a traveling sideshow: jugglers, fire-eaters, fortune-tellers, tumblers, actors and freaks. And among them are the mysterious and handsome Jack, who does fiery monologues from Shakespeare, friendly Annie, who is the world's fattest lady, and Sprat, the boy they've found starving in a ditch. Except . . . that Sprat is really 16-year-old Zoe who has run away from her evil aunt and lecherous cousin and thrown herself in fortune's hands.

In Playing the Jack Zoe undergoes three transformations. In addition to being Sprat, she becomes Gemini, who is abducted by the owner of a notorious child brothel, and finally Esther wh she takes the place of a young woman who is to attend a finishing school for housemaids and paid companions. What holds these diverse sections of the novel together is the romance between Zoe and Jack. What begins as an adventure story replete with period-piece details, ends with a finale in the best of Gothic traditions with a mad wife hidden away, a fire and a tragedy before the lovers are united to live happily ever after.

The plot is a fantastic one, but what makes it work is author Brown's meticulous research into 18th-century Britain and her obvious enthusiasm for the era and its mores. There is a richness in this first novel that far outweighs the trivialities of what is essentially the Cinderella story in yet another garb. THE SIXKILLER CHRONICLES. By Paul Hemphill. Macmillan. 243 pp. $16.95.

THE Nashville Music scene forms the backdrop for this multi-generational novel about a family of hillbillys, the Clays of Sixkiller Farm. Bluejay, who comes from a long line of hard-drinkin', moonshine-makin', preachin' and singin' Clays, becomes a fixture on the Grand Ole Opry stage and a country singing star with his own traveling band. Along with his sidekick, the Cherokee Indian Sam Sixkiller, Bluejay bears whatever fortune deals to him with irreverence, a fierce independence and a goodly swig of moonshine. The death of his wife, his son's disastrous marriage and alcoholism, and the threat of a developer trying to take over Sixkiller Farm can't subdue Bluejay's spirit. Even at the end of his life, he's belting out songs, taking to the road and becoming a cult figure to a generation of Yuppies who don't know Nashville from Louisville.

Hemphill, author of The Nashville Sound, writes authoritatively, lovingly and vividly about Bluejay and the beginnings of country and western music, but he is unable to sustain the quality as the novel heads into the stories of his son Jaybird, a failed music promoter, and his grandson Robin, a Harvard- trained doctor. With each succeeding generation, the characters get blander, the prose loses more of its color and the plot line gets thinner until it ends in a maudlin deathbed scene with all the Clays gathered at Bluejay's side. The Sixkiller Chronicles could have been a fine novel if author Hemphill had focused on one protagonist rather than three. OTTO'S BOY. By Walter Wager. Macmillan. 263 pp. $16.95.

THE mass killer is the subject of this fast-paced thriller. After World War II, Anna Henke, the widow of SS officer Otto Henke and mother of a small boy, married an American GI and moved to United States. In spite of her marriage and change of citizenship, she harbored the most extreme of Gestapo philosophies, an attitude she has passed on to her son, Ernest, along with a fear of sexuality and an inordinate devotion to cleanliness. A repressed childhood featuring sadistic beatings and enforced enemas have turned Ernest into a maniac whose aim is to rid New York City of its blacks, Jews and Hispanics and anyone else who isn't part of the Aryan race.

But an in-depth study of Ernest's insanity is not the point of Otto's Boy. Instead, the books focuses on how he plans and implements his mad acts of genocide. How did he get hold of a nerve gas so potent that it instantaneously kills 117 people in a subway car between the Columbus Circle Station and 125th Street? When it turns out the the nerve gas is manufactured by the U.S. Army and kept under intense security, how did he manage to steal it? And, how and where will he strike again? Police detective David Bloom stalks Otto's Boy through the streets of Manhattan and the files in Washington, battling against the maniac's deadlines, the stupidity of the FBI and the bureaucracy of New York's finest. Lots of action, a little bit of sex, enough mayhem to keep you breathless. CHICAGO GIRLS. By Edith Freund.Poseidon. 427 pp. $16.95.

ONCE pon a time, before the income tax law and the formation of labor unions, there was an American aristocracy whose wealth was accumulated by the toil of poorly paid, poverty-stricken workers. From these two strata of society come two Chicago girls: heiress and suffragette Margaret Marsh, and Gertrude (Trudy) Jahn, whose 13- member family lives in three rooms and whose immigrant father works in the stockyards.

Beautiful Trudy runs away from home, finds a lover and joins the select group of kept women who are traded from one wealthy man to the next. She ends up in the notorious Playhouse where the married men of Chicago's wealthiest class hide their mistresses. There, she becomes addicted to drugs, and her sinister lover, Jay Darling, leads her deeper and deeper into sexual vice. In the meantime, Margaret, equally beautiful but far more pure, struggles to find some identity in the stifling hot-house atmosphere of Chicago society. She falls, reluctantly, in love with a young man called Stephen, who appreciates her intelligence, her education and unconventional thinking.

Unfortunately, Chicago Girls is one of those books whose total does not equal the sum of its parts. First-novelist Freund has created two sympathetic heroines, can write a fast-paced narrative and is capable of describing Victorian society with a subtle and pointed humor. Yet the stories of Margaret and Trudy rest uneasily beside one another, coming together only at the novel's end where an unlikely denouement attempts to resolve the plot in an overly romantic fashion. The result, an interesting, but inconsistent novel.