Watching impressive new star Harry Hamlin as Perseus in the flawed but often captivating mythological adventure fantasy "Clash of the Titans," you can appreciate how much progress has been made in the area of costume movies over the course of a generation.

In addition to his natural photogenic advantage, Hamlin brings disciplined skills and an astute camera sense to his portrayal of a mythic hero. Like Christopher Reeve in "Superman," he doesn't miscalculate effects or defy belief and rises to the spirit of idealized behavior without losing intimate human contact or exaggerating noble gestures.

Reeve, however, gave Superman a humorous dimension that Hamlin lacks as Perseus. While Divine despots conspire to keep Perseus wonder-struck and preoccupied, it would be an improvement on an otherwise stirring performance if Hamlin occasionally lightened up.

Hamlin is always a magnetic pressence. His heroic intensity is essential to the effectiveness of the key action sequences. Here, the actor is obliged to look convincing while fighting creatures designed by the noted modelmaker and stop-motion animator Ray Harryhausen and then matched optically with the live-action footage. In the spine-tingling Medusa sequence, the high point of the show, Hamlin establishes riveting eye contact from the start, raising his shield just below eye level and moving into Medusa's infernal cave.

The gesture makes you eerily conscious of the principal death threat facing Perseus and his companions: Medusa's glare. Throughout the sequence Hamlin's eyes serve as a suspense-tightening beacon. By the time Perseus and Medusa draw near each other and he prepares to take the blind, all-or-nothing swing of his sword, your sense of intimacy with the hero is almost unbearable.

Although "Titans" is similar in style and spirit to the fantasy films Harryhausen and producer Charles H. Schneer have been making for over 20 years -- "Jason and the Argonauts," "The Seventh Voyage of Sinbad," "Sinbad and the Eye of the Tiger," etc. -- it seems a classier operation in several respects. For example, it's a kick to discover Laurence Olivier on Mt. Olympus, impersonating a sneaky, strong-voiced Zeus, a most welcome departure from his recent string of frail codgers. Olivier is surrounded, in oddly stiff theatrical poses, by a formidable set of goddesses: Claire Bloom as Hera, Maggie Smith as Thetis and Ursula Andress (curiously underutilized) as Aphrodite.

The title is a fake-out. The Titans have been subdued and imprisoned by Zeus well before the beginning of the story devised by screenwriter Beverly Cross (Maggie Smith's husband, incidentally), embroidering the Greek legends with intermittent wit and eloquence. "Clash of the Titans" depicts the trials of Perseus, a favorite illegitimate offspring of the philandering Zeus, as he races against time to save his beloved, Princess Andromeda, (Judi Bowker) from being sacrificed to a sea monster.

The humans are manipulated by the double-dealing deities on Mt. Olympus. The script could probably use even more of the amusing Olympian treachery, with Zeus trying to fix things for Perseus while Thetis is busy making life horrifying for the brave young mortal.Cross has introduced an effective element of romantic conflict, ascribing Thetis' hatred of Zeus to his banishment of her son Calibos, Andromeda's intended before the angry god transformed him into a half-beastly outcast.

Hamlin and Bowker make a beautiful screen couple. At the same time there's an undercurrent of tragedy in their attraction. Both the miniature sculpted by Harryhausen and the grotesquely made-up figure embodied in close shots by actor Neil McCarthy endow the wretched Calibos with dignity and sexual potency. It's easy to imagine Andromeda loving him before the shocking transformation imposed by Zeus.

Harryhausen has always excelled at suggesting innate, blighted beauty and nobility within his ferocious monsters. His Medusa projects the same terrigying pathos. She's a female counterpart of Calibos, the nightmarish distortion of a once beautiful, imperious woman. Harryhausen fell in love with the movies when he saw "King Kong," and the best of his creations pay homage to that inspiration.

Harryhausen is not as successful with less demonic figures. A little mechanical owl called Bubo proves a rickety comic-relief embarrassment, inevitably suggestive of R2D2 but utterly expendable. There's a bad hitch in the scenes depicting Perseus taming the winged horse Pegasus. Harryhausen's winged model appears in long shots, and the cuts to a real horse in close-up conspicuously obscure him from the neck back. The Frequency of the crosscutting probably puts excess pressure on an illusion one might play along with if kept entirely in animation.

The quality of shooting varies radically from scene to scene. You get the impression that the budget was lavished on strategic sequences, like the Medusa episode, leaving many others in patchy condition. It might be unwise to see "Titans" too soon after an adventure movie as exciting as "Raiders of the Lost Ark." While "Titans" stirs satisfying romantic and heroic feelings every so often, usually with the aid of Laurence Rosenthal's rich, expansive score, the appeal -- harking back to the 1940 production of "The Thief of Baghdad" -- is quaint and stilted.