Peter Yates' "Krull," now at area theaters, is an elaborately lackluster attempt to fabricate a fresh adventure fantasy out of a batch of familiar genre ingredients.

Unfortunately, the synthesis that results doesn't have much in the way of sustained excitement or the distinctive tang of the fabulous. While perfectly presentable and agreeable, especially if you are in an undemanding frame of mind, "Krull" remains a thin, dogged exercise in extravagant adventure.

The title refers to a fanciful planet threatened by subjugation from a superhuman invasion force, robotic-reptilian warriors known as Slayers, who march at the command of a colossal demon, the Beast. The patriarchs of Krull's two preeminent, warring families have grudgingly agreed to bury the hatchet in the interests of self-preservation. A marriage ceremony unites the prince of one house, Ken Marshall as valorous Colwyn, with the princess of the other, Lysette Anthony as saucy Lyssa. And not a moment too soon. Seconds after the knot is tied in a magical ritual of fireball-handling by bride and groom, the castle is attacked by a Slayer war party, which succeeds in abducting Lyssa and leaving Colwyn wounded among the corpses of his knights, kinsmen and brand-new in-laws.

Subsequent events lead the bereft but brave prince in pursuit of the Beast's lair, a flying mountain called the Black Fortress that defies detection by picking up and vanishing, through the courtesy of lap dissolves, to new locations every dawn. Colwyn's quest is aided by several companions, beginning with Freddie Jones as Ynyr, a reclusive old knight who serves as the resident Obi-Wan Kenobi, and encompassing a band of outlaws under the leadership of Alun Armstrong; an inept magician played by David Battley (sidekick in charge of comic relief, and exceedingly slight, amateurish relief it tends to be); and a gravely dignified, melancholy Cyclops, impersonated by Bernard Bresslaw in a mask that looks somewhat fake but accommodates a good effect: the peculiar sight of one eye blinking.

Naturally, several preparatory adventures test Colwyn and his new comrades before the showdown with the Beast. The hero must retrieve a magical, jeweled weapon called the Glaive, a kind of five-pronged switchblade that operates like a flying, miniature chainsaw, from an apparently volcanic stream. The party must navigate a bran-flaked swamp while outfighting a Slayer patrol. Ynyr must pick his way along an enormous spider web while seeking necessary intelligence from a forbidding hermit called the Widow of the Web (Francesca Annis in wizened makeup), who turns out to be a lost love.

All these episodes and characters seem serviceable enough in theory, but they fall short in practice. None of the actors projects sufficient glamour or authority to give the material adequate heroic or romantic oomph. For example, Marshall betrays so little reaction when plunging his arm into that fiery stream that you feel conned by the setting; maybe that was a pool of Kool-Aid the Glaive was resting in. There appears to be a vast technological disparity between the medieval weaponry of the Krullians and the hi-tech swords of the Slayers, which convert into laser guns when flipped backwards or something silly; luckily for the good guys, the Slayers don't seem to exploit this advantage at close quarters, so their heavy-limbed swordplay permits them to be out-dueled with pathetic consistency in hand-to-hand combat. In the clutch, they're as ponderous as the Cylons in "Battlestar Galactica."

Production designer Stephen Grimes has succumbed to obvious influences from "Alien" in envisioning both the Beast and his fortress, but the psychosexual sliminess and creepiness that animated "Alien" is never reawakened in the setting of "Krull." The corridors are conspicuously bony or sinewy, but these innards are too polished and ornamental to evoke sinister, primordial apprehensions. The sadistic sensuousness of the "organic" set design in "Alien" gives way to a decoratively plastic variation in "Krull," which doesn't raise much of a sweat in either erotic or cliffhanging terms. KRULL

Directed by Peter Yates; music composed by James Horner; director of photography, Peter Suschitzky; production designer, Stephen Grimes; visual effects supervisor, Derek Meddings; written by Stanford Sherman; executive producer, Ted Mann; produced by Ron Silverman. Rated PG. THE CAST Colwyn .... Ken Marshall Lyssa .... Lysette Anthony Ynyr .... Freddie Jones Widow of the Web .... Francesca Annis