BRIAN JACQUES' Redwall (Philomel, $15.95; ages 10-up) tells a familiar story of good-hearted folks of a romanticized medieval era being threatened by a despoiling horde. The catch here is that the monks of Redwall Abbey are mice, and the villains an army of rats, ferrets and weasels. A supporting cast of badgers, squirrels and other furry creatures live in surrounding Mossflower Wood, which creates a strong suggestion of Kenneth Grahame, especially in a hearty banquet scene in the opening chapters.

Jacques' novel runs to 351 pages, offering a highly detailed picture of life in Redwall and the campaign for its defense. It is asking a lot to bring the scope and density of a novel to so whimsical a notion, which perhaps only a writer with the imaginative force of Grahame could sustain past the length of a bed-time story. The narrative weight of Redwall consistently raises questions the reader is not supposed to think about. If all the woodland animals can talk and live in peace, what about the big salmon they caught for the banquet? And what does an order of fieldmice worship?

Redwall never resolves the dissonance inherent in combining the trappings of small children's stories with the texture and particularity of a long narrative. In such a context, the convention of the various woodland animals being dependably kindly, treacherous, or ill-tempered according to their species develops -- like Tolkien's dwarves, elves, and "men" -- inescapable racial echoes, which Jacques unfortunately compounds in assigning one animal the kind of comical pidgin ("Killee pretty quick, you betcha") that British popular fiction once commonly ascribed to foreigners. Other touches -- the hero of the story is a young novice mouse who is seen in the first chapter dreaming of heroic deeds, and ultimately saves the day with the recovery of a legendary sword -- suggest that Jacques, whose background is that of radio storyteller and playwright, is most familiar with material better suited to some other form than a full-length novel. Unfortunately, Redwall is announced as "the middle volume of a trilogy about the Redwall mice."

DIANA Wynne Jones always knows what sort of story she is telling, although A Tale of Time City (Greenwillow, $11.75; ages 10-up) marks her first venture from fantasy into straightforward science fiction. Beginning with a grimly realistic account of an evacuation of children from London during World War II, the story veers abruptly when 11-year-old Vivian is kidnaped by a young man who claims to be her waiting relative, but whisks her off in what proves to be a time machine.

Vivian's abductor, a self-assured boy named Jonathan, takes her to Time City, a futuristic metropolis that lies outside time and space, whose denizens travel freely through history. The city is facing a crisis, and Jonathan has mistaken Vivian for the woman who may hold its key. Or possibly he has not, for both children catch a glimpse of their future selves hurrying on some mission of urgency.

The rest of the novel develops an impressive series of time paradoxes and plot complications, which Jones meticulously unravels in her final chapter. This generates a great sense of busyness, perhaps too much for the novel's good.

Like all of Jones' books (among them, Archer's Goon and The Homewardbounders), A Tale of Time City is witty, well-peopled, and full of Jones' appealing sense of keeping one's head amidst chaos.

Robert Westall's novels and stories are set in the villages and rural areas of England, little known corners (at least to young Americans) such as Garmouth, Dorset, or Northumberland, which Westall evokes with a powerful sense of atmosphere and place. Rachel and the Angel and Other Stories (Greenwillow, $10.25; ages 8-up), collects seven stories, all but one fantasies set in the English countryside. The exception (which almost proves the rule) deals with a British landscape painter given a commission on another planet, who creates chaos in trying to bring his English world along with him.

The shortest stories in the volume seem too slight, tours of colorful places -- a windswept hill covered with ancient cairns; the salt mines of Northwich with their strange history -- woven into thin or perfunctory tales. The two best stories, "Rachel and the Angel" and "A Nose Against the Glass," confront ordinary people with supernatural agents (perhaps imagined) that reflect back their own flawed nature. Rachel, a vicar's daughter who encounters an angel in her father's church, defends her village against a judgment of destruction, and has her nose rubbed in the pettiness and sins of her neighbors. The story may be read as an adolescent girl's projections of her anxieties about adult sexuality and the American jets flying too low over her village, or as fantasy.

In "A Nose Against the Glass," an elderly antique dealer, grown bitter and loveless, looks up on Christmas Eve to see a small face pressed against his window. Westall handles what might be called the Dickens theme with no real surprises, but gives the life of his protagonist and the surrounding village a richness and particularity that makes for a dense and effective story.

PAT O'SHEA'S previous book was the very long young adult fantasy The Hounds of Morrigan, but with Finn MacCool and the Small Men of Deeds (Holiday House, $12.95; ages 8-up), the author shows that she knows exactly how long a story should be. In retelling one of the legends of Fionn MacCumaill (she politely explains her modernization of the name in an author's note) O'Shea uses wit and a light irony to enliven a story that might otherwise seem best read aloud to toddlers. "The Norsemen used to work themselves up for mayhem and murder when sitting round their great winter fires, toasting at the front while their backs were freezing, listening to stories of how their fathers and grandfathers were this, that, and the other... and be filled with the desire to carry on the family business."

The story, like most folk tales, advances with an easy inevitability -- as soon as Finn agrees to help a King of the Giants prevent the theft of his last child, he meets eight little men who each display a remarkable ability, which even the youngest reader can guess will prove helpful in the imminent adventure. Only one scene -- where the heroes crowd round the cradle waiting for their invisible enemy to strike -- carries any real drama, although O'Shea makes the most of it. What the story lacks in internal conflict, however, it makes up in color, and nicely captures the essential sunniness of the Fionn MacCumaill tales.

M.J. Engh has also written one substantial novel (the political science fiction novel Arslan) before turning to a smaller compass, and The House in the Snow (Orchard Books, $11.95; ages 8-up), whose 120 pages describe a single uninterrupted narrative, is essentially pre-Renaissance Europe, though not the idealized arcadia of dragon tales or children's movies. Outside an isolated village lies a mysterious house, which has no visible inhabitants although smoke rises from the chimney and lights shine in the windows. Shunned by frightened villagers, the house stands unapproached for decades until Benjamin, a young orphan fleeing an intolerable master, ventures upon it on a snowy night.

Benjamin discovers an even younger boy, Mackie, who is fleeing away from the house. He learns that the house is inhabited by a gang of bandits, who own -- it is the novel's single fantastic element -- something that allows them to become invisible. They are served by an entourage of kidnapped boys, who in time join their ranks. Mackie has fled after overhearing that the invisible guards would be off-duty during the course of a revel that night. As an alternative to freezing to death, the boys decide to return to the house and try to surprise the bandits.

Their story and implausible success are told in a careful, lucid prose that creates a vivid sense of immediacy. Engh pays close attention to the mechanics and implications of the protagonists' every step, and achieves verisimilitude through numerous small touches (as when one of the boys who joins them realizes that the relieved guards must still be wandering invisible, so that their prisoners would not see all the bandits at once and know themselves to be unguarded). In a concession to her young readers, Engh makes the rebellion rather less bloody than plausibility would require; there is a good deal of bad guys being knocked on the head and trussed up. Nevertheless, The House in the Snow is an unusually intelligent and well-written book, and prompts the hope that Engh -- whose previous novel and stories have been intended for an adult audience -- writes more fiction for young readers.

Gregory Feeley writes frequently about fantasy and science fiction. He is completing a novel entitled "The Oxygen Barons."