Of all the literary and cinematic genres, fantasy ought to come closest to plumbing the depths of the human mind. Its rules are the rules of dreams, its monsters the stuff of nightmares. But with rare exceptions — the 1933 “King Kong” comes to mind — few live-action fantasy films have taken full advantage of the genre’s possibilities. The release of two eagerly anticipated fantasy films, “The Lord of the Rings: The Fellowship of the Ring” and “Harry Potter and the Sorcerer’s Stone,” may change all that, making this the winter of the wizard.

For readers, actually, it’s been wizard time for three years or five decades, depending on when you start counting — from the publication of the first of J. K. Rowling’s Harry Potter books, in 1998, or from the early 1950’s, when their ancestor J. R. R. Tolkien’s trilogy, “The Lord of the Rings,” appeared. Both cycles set an epic struggle between good and evil among magicians and mythological creatures. They share not only a genre and a central theme but the fanatical devotion of hordes of readers whose fervent attention to every detail of the fictional world hovers between longing and faith. The film versions of the two sagas promise to challenge and expand those obsessions.

“The Fellowship of the Ring,” which opens on Dec. 19, is only the first serving of the director Peter Jackson’s interpretation of the epic, with two more films to follow. With the producers Barrie M. Osborne and Tim Sanders, Mr. Jackson and his wife and co-writer, Fran Walsh, set in motion a project of extraordinary scope. All three films were shot simultaneously in Mr. Jackson’s native New Zealand. That meant actors like Elijah Wood, who plays the hobbit Frodo Baggins, the story’s diminutive, furry-footed hero; Ian McKellen, who plays the wizard Gandalf; and assorted elves (Cate Blanchett, Orlando Bloom, Liv Tyler), dwarves (John Rhys-Davies) and human warriors (Viggo Mortensen, Sean Bean) lived for up to a year in Mr. Jackson’s antipodean Middle Earth.

Sir Ian says he was originally “somewhat apprehensive about spending an entire year away from home, but it ended up being the most fulfilling and enjoyable job that I’ve had in 40 years of professional acting.” Filming all three movies at once offered the filmmakers consistency and economies of scale, but at a reported $270 million ($90 million per installment), it was a huge commitment on the part of the studio, New Line Cinema.

Eventually, the Harry Potter saga will be even longer than “The Lord of the Rings.” Ms. Rowling has planned seven books set at the Hogwarts School of Witchcraft and Wizardry, although only four are written so far. Since her main characters begin the series as 11-year-olds and age one year per book, making several books into films simultaneously would not be practical, says the director of the first one, Chris Columbus. “Harry Potter and the Sorcerer’s Stone,” the opening segment, is scheduled for release on Nov. 16; Warner Brothers also has plans to film the next book, “Harry Potter and the Chamber of Secrets.”

Warner Brothers chose Mr. Columbus, the director of “Home Alone,” for the first Harry Potter film after negotiations with Steven Spielberg fell through. Part of Mr. Columbus’s appeal was his skill and experience working with child actors, says the producer, David Heyman. Finding the right Harry was harder. “We began looking in November of 1999,” Mr. Heyman says. “By July of 2000 we still hadn’t found our Harry.” Mr. Columbus had seen the young British actor Daniel Radcliffe in a BBC adaptation of “David Copperfield,” but he was said to be unavailable. Then Mr. Heyman, who is British, went to the theater in London with Steve Kloves, the screenwriter, and spotted a potential Harry in the audience.

“I saw this boy who combined a wonderful sense of curiosity, openness and generosity with a warmth that wasn’t sentimental or too cute,” Mr. Heyman says. “He seemed accessible — an Everyboy. While I was staring at him, I heard my name, and next to him was a man I knew, Alan Radcliffe. He introduced me to his wife, Marcia, and his son, Daniel. The play was a blur — I kept looking behind me at Daniel. I called the next day and said, `Alan, your son! Would you allow him to audition?’ ” Mr. Heyman persuaded the parents to let Daniel become Harry Potter.

Most of the other child actors were newcomers to film, Mr. Columbus says. “We were looking at a real sense of freshness.”

Adults include Fiona Shaw as Harry’s horrid Aunt Petunia; Maggie Smith as the stern but fair deputy headmistress, Minerva McGonagall; and Alan Rickman as the sinister potions professor, Severus Snape.

Bringing freshness to “The Fellowship of the Ring” is a much harder task, given the 50 years of influence it has exerted on the genre.

When J. R .R. Tolkien wrote “The Lord of the Rings” in the years after the Second World War, he meant to create a pre-medieval mythology for the English people, believing that their linguistic and narrative heritage had been ravaged by the Norman Conquest nine centuries earlier. An outspoken enemy of technology, Tolkien longed for an England before the invention of engines, especially engines of war. Still, the smoldering incantatory fire that his story lighted in readers’ imaginations had by the 1970’s exploded, scattering dwarves, elves and — most of all — wizards across story lines and media that would surely have made the tradition-minded scholar cringe. Blame Tolkien for resin figurines of bearded elders carrying crystal-headed staffs and for armies of elven horsemen charging across a computer screen at the flick of a joystick.

Blame him, too, for Harry Potter. Of course, the orphaned boy who develops his magical powers at Hogwarts has many ancestors. Ms. Rowling writes in a tradition of British children’s fiction that embraces school stories like Geoffrey Willans’s satirical Molesworth books, set at a school called St. Custards; and fantasy like the Narnia chronicles, by Tolkien’s friend C. S. Lewis, which sent ordinary children through magical portals to fight evil in a world of witches and talking beasts. Nevertheless, “The Lord of the Rings” casts such a shadow over the genre it created that Harry Potter could hardly exist without it.

Since filmmakers have had nearly 50 years in which to tackle “The Lord of the Rings,” the timing of this production seems striking. Is Tolkien flying from page to screen on Ms. Rowling’s robe-tails? Unlikely, as an executive producer, Mark Ordesky, points out: Mr. Jackson had been working on “The Lord of the Rings” for two years when Ms. Rowling’s first book was published. Still, he says, the two projects have complemented each other. Mr. Heyman, too, sees the films as companions in arms, not opposing forces. “I hope `The Lord of the Rings’ is brilliant,” he says. “It can only serve us well if it is.”

Is the timing just a coincidence, then? Or is some more magical power at work — does some sorcerer have the zeitgeist in thrall? It’s not magic, says Mr. Jackson, but the very force that Tolkien so loathed — technology. “About five years ago, I developed a couple of movies using computer effects, and I began thinking about what projects could make use of this groundbreaking effects technology,” he says. “I wanted not just special-effects-driven films but films that actually had stories. `Lord of the Rings’ came immediately into my mind. Previously only a cartoon version was made, because the technology didn’t yet exist to make a realistic live-action film.”

Mr. Jackson’s explanation, practical as it is, goes only so far. After all, Willis O’Brien didn’t need computers to make King Kong bat airplanes out of the sky when he created the special effects for that movie in 1933. Filmmakers have been representing imaginary elements from the medium’s earliest days, developing their audience’s expectations as they go. Someday the Balrog — a cave demon conjured from computer-generated lava and flame, in which Mr. Jackson and his collaborators take great pride — may seem as technologically crude as George Reeves, television’s Superman, flying against a projected backdrop with his arms stretched out, his cape flapping in the wind of a fan.

The experience of Mr. Columbus goes a long way to explaining the timing of the two fantasies. Mr. Columbus credits his daughter Eleanor, then 10, with bringing him to the project by insisting that he read the book. Engrossing as they are, the Harry Potter books are not the first children’s fantasy novels worthy of adult attention. Their crossover success probably has a lot to do with demographics — armies of Eleanors pestering their parents. Those passionate fans place an extra burden on both films.

Authors and readers as careful as Tolkien, Ms. Rowling and their fans require equally meticulous filmmakers. Tolkien, a philologist, invented entire languages, complete with grammar and writing systems, for his elves, dwarves and other races. “When we made an inscription, we couldn’t just scratch out some writing,” Mr. Ordesky says. “There are people out there who can read Dwarvish. We had to make sure it was correct.”

IN “The Lord of the Rings,” Frodo Baggins, a young hobbit — hobbits are a home-loving race fond of their gardens and cozy underground homes — is given a grave and dangerous responsibility. He must destroy the Master Ring that gives its wearer dominion over all the inhabitants of Middle Earth, before it falls into the hands of Sauron the Dark Lord, who forged it long ago and then lost it. As Sauron searches for the Ring with all the resources of a well- staffed inferno, Frodo sets out with a small retinue of dwarves, elves, men and hobbits under the guidance of Gandalf. Their goal: To carry the Ring into Mordor, the Dark Lord’s own territory, and there destroy it by throwing it into the fires of Mount Doom, where it was forged.

In “Harry Potter,” the young wizard takes on the Frodo role, with a bit of Gandalf thrown in. Like Frodo, Harry is a person of small stature and more or less ordinary gifts (for a wizard, anyway). What sets him apart from the other students at Hogwarts — aside from his skill at Quidditch, a sport that seems made for special effects, played on flying broomsticks with three kinds of magical balls — are his courage, called forth like Frodo’s at moments of dire necessity, and his destiny, entangled like Frodo’s with that of the saga’s Dark Lord. When Harry was only a baby, his parents died fighting the evil wizard Voldemort. Harry escaped with his life, but Voldemort’s misfired curse left a scar shaped like a lightning bolt across his forehead and tied the older wizard to the baby with bonds of fear and revenge. Harry lives with his unpleasant and decidedly unmagical aunt and uncle — portrayed by Fiona Shaw and Richard Griffiths — until the year he turns 11, when he’s summoned to Hogwarts to prepare for his enchanted destiny.

Ms. Rowling’s vision differs from Tolkien’s at several key points. Where Tolkien invented an entire world separate from our own — or perhaps, as Mr. Jackson suggests, the ancestor of it — Ms. Rowling tucks her magical world into the interstices of the universe where “muggles,” or nonmagical folks, go about their humdrum business. Much of the film was shot on location in the United Kingdom, including scenes at the King Cross railroad station in London as young wizards set out for school. Wizards dress in robes and pointy hats, write with quill pens and send messages by owl instead of post. They find muggle fashions and technology — sneakers, telephones — utterly mystifying.

Like the contrast in “Lord of the Rings” between the homely Shire, where hobbits live like villagers in a Thomas Hardy novel, and the exotic forests, mines, plains and mountains where the bulk of the adventure takes place, the distinction in the Harry Potter story between the muggle and wizardly dominions makes it easier for the audience to identify with the young hero.

LIKE Harry at the beginning of the story, we’re confined to a muggle world despite the magic within us. Surely we, too, deserve to express our inner marvels and save the world while we’re at it.

The contrast between the two domains also provides a vantage point from which Ms. Rowling towers over her predecessor: humor. In both the book and the movie, the hobbits are genial enough in their lighter moments. In the movie, the size difference between them and the wizards gives Sir Ian some fine opportunities for slapstick, as low-hanging chandeliers and ceilings menace Gandalf when he visits Hobbiton. Nevertheless, Tolkien does better with grand battles than repartee. Samples of the film’s action sequences show perilous drops over yawning chasms or faceless, demonic horsemen in billowing cloaks barely missing the heroes; the audience is clearly meant to gasp, not giggle. Parallel scenes from “Harry Potter,” although potentially just as scary, are infused with funny surprises. This is, after all, a film in which a nearly headless ghost — a small flap of skin keeps him out of the headless ghosts’ club — is played by the comedian John Cleese.

Ms. Rowling helped shape the film from the beginning, says Mr. Columbus, a fact that he expects will be helpful in satisfying the fans. “She’s probably the most useful collaborator you could have,” he says. “Jo Rowling was always available, without ever being prohibitive,” Mr. Heyman adds. “She can tell you the 12 uses of dragon blood, or the color of the tapestry in the Gryffindor common room. She had great ideas. It was her idea to cast Robbie Coltrane as Hagrid the groundskeeper.”

With an older book and a more mature fan base, the Tolkien team faced a different challenge. In the master’s absence, Mr. Jackson was free to make his own interpretation of the book, although he, too, claims to have stuck as closely as possible to what he understood of the author’s intention. Mr. Jackson set about it by using technology and artifice to make technology and artifice seem to disappear. “People somehow think that because it’s fantasy, it doesn’t have to be real, and I think that’s a huge mistake,” he said. “If it looks too stylized or fake, the audience isn’t going to buy into it. We built the set where the hobbits live a year before we started shooting, rather than the typical three weeks. During that year we planted the gardens. We put cabbages and carrots in, we put hedges in, we planted grass seed and weeds, so after a year the entire place had grown and looked completely real.”

Rather like an ecologist reintroducing locally extinct bears and wildcats, Tolkien borrowed from the Scandinavian and other European myths and invented his own natural spirits, such as the treelike Ents, to repopulate England’s imagination. He was passionately attached to his homeland. But to create an English Middle Earth, Mr. Jackson says, he had to move Tolkien’s story around the world to his own native New Zealand, where he found a temperate, European-looking landscape not yet laced with roads and strung with telephone poles.

THE quest for realism extends to the acting. Mr. Jackson wanted people, not archetypes. “I hate the idea of guys with pointy hats who can fire lightning out of their fingers,” he says. Although Tolkien described Gandalf as an immortal sent to Middle Earth in the body of an old man, Sir Ian emphasizes his human aspect. “What you’ll see on screen is someone whose supernatural qualities are guiding his will and purpose but not his everyday existence,” he says.

With Sir Ian playing the testy wizard, the film has as good a chance as any of avoiding a pointy-hatted cliché. The Harry Potter team has the advantage of hindsight here. Knowing all about the clichés, Ms. Rowling was able to play with them. She even built a hat into her story as a character. (It sorts incoming Hogwarts students into the school’s four houses.) Designers have followed her subtly satirical lead, making robes and broomsticks, potions and wands seem as ordinary and kid-like as sneakers and basketballs.

Even so, there’s nothing like an original — whether a fantasy, a wizard, or even a hat. “Ah, yes, the hat,” Sir Ian says. “It was always useful for making me feel like Gandalf. It’s such a potent image of a wizard, and there are many references in Tolkien to it. Gandalf loses his hat in the Mines of Moria when he takes on the Balrog. His character undergoes a transformation, and afterwards he doesn’t wear it.” Like the Ring itself, the hat is a powerful symbol, but it’s also practical: “Without the hat,” Sir Ian says, “you have a problem of what to do with all the hair.”