One would imagine that Jeremy Irons might have learned from his appearance in “Dungeons & Dragons” (2000) to avoid sword-and-sorcery pictures. Yet here he is in one again. True, “Eragon” is based on a popular series of books rather than a role-playing game, and perhaps he saw it as closer to “The Lord of the Rings” than to his earlier genre misfire. And in this case he’s playing a good guy–the Gandalf, so to speak, or Obi-Wan Kenobi figure–rather than the Saruman or Darth Vader one. But unhappily the result isn’t much better than his initial foray into such stuff.

Christopher Paolini, the author of “Eragon” was, of course, but a teen when he began writing the book, so it’s not surprising how derivative the story is. It’s essentially a repeat of the first episode of “Star Wars” dropped into a “Lord of the Rings” context. The titular hero is, like Luke Skywalker, a farmboy adopted by his uncle Garrow (Alun Armstrong)–though in this case his mother is supposedly still alive somewhere. The family, which also includes Eragon’s cousin Roran (Chris Egan), lives under the tyrannical rule of the evil King Galbatorix (John Malkovich), whose chief henchman is a mystical sorcerer named Durza (Robert Carlyle). (It’s not difficult to see the templates of Emperor and Darth Vader in this duo.) Galbatorix, we learn, came to power by betraying his fellow dragon riders, who were apparently the Jedi of their land, each pledged to battle evil-doers aboard his personal flying dragon.

Lo and behold, when beauteous Arya (Sienna Guillory), the guardian of the last dragon egg, is pursued by Durza, she transports it to a forest where Eragon just happens to be hunting, and it hatches for him–the sign that he is the dragon’s destined rider, and soon the darling little beastie grows into Saphira (voiced by Rachel Weisz), with whom he can converse telepathically. Luckily for the untested youth, he’s quickly befriended by Brom (Irons), a local coot who turns out to be a former dragon rider himself. He trains Eragon while escorting him to the Varden, a group of rebels led by Ajihad (Djimon Hounsou), who have been awaiting a promised warrior to inspire to them to take up arms again. There are adventures and battles along the way, of course, since Durza is out to kill both boy and beast, especially since Eragon is determined, despite the risks, to free the captured Arya from the sorcerer’s clutches. Fortunately they find an ally in the swashbuckling youth Murtagh (Garrett Hedlund). There’s a big battle at the end in which Eragon proves his mettle by taking on the evil Durza one-on-one (or two-on-two, if you count the dragons).

This mixture of Lucas and Tolkien might be exciting on the printed page, but Peter Buchman’s adaptation is prosaic, beginning with a line for Galbatorix which immediately invites an unintentional giggle and going on to include a whole series of pompous pronouncements for Brom that turn him into an insufferable windbag. (Irons makes it worse by reciting them straight, without the saving touch of self-deprecating humor that Alec Guinness brought to Obi-Wan.) And in the hands of director Stefen Fangmeier (whose name really sounds as though he should be helming Dracula movies), the whole thing comes across as plodding and rather dull. It certainly doesn’t help that the physical production looks pretty chintzy (although the eastern European locations have a certain grandeur) and that the effects are, by the highest standards, only fair. (Ray Harryhausen’s dragons may have been more stilted than Saphira, but they had more personality, and weren’t burdened by Weisz’s pedestrian vocal delivery.) The cinematography by Hugh Johnson is okay, though some of the night scenes are awfully murky, but Patrick Doyle’s score sounds tepid and recycled.

The human performers are variable. Irons hams it up badly, but he’s a piker compared to Carlyle (who, with his long stringy hair looks a bit like Bette Davis in “Whatever Happened to Baby Jane”–and masticates the scenery as much as she did, too), and Malkovich, who has only a few brief scenes but is so over-the-top you’re glad he doesn’t appear in more. By contrast Hounsou is very restrained, perhaps embarrassed (and rightly so) by the outlandish costumes he’s forced to wear. As for the youngsters, Guillory and Hedlund are energetic enough, and Speleers, a handsome lad making his professional debut, gets by, even though he seems more model than actor and lacks real charisma. (He doesn’t look all that comfortable in his costumes, either.) The lesser parts are more often than not filled very poorly, with the young woman briefly playing a fortune-teller (Joss Stone, is it?) not only miscast but almost unbelievably amateurish.

It goes without saying that the movie closes with the promise of a sequel as Galbatorix calls forth his own dragon just as the credits roll. But one really has to wonder whether, despite its popularity on the printed page, this pallid first installment of Paolini’s projected trilogy will find enough favor with filmgoers, even the book’s biggest fans, to merit continuation. Repeat business seems unlikely, and the DVD shelves beckon. “Eragon” will probably be gone ere long from theatres, and when the grosses are tallied, there may be little call for the survivors to take up their swords–and dragons–a second time.