`APT PUPIL' SHOWS US THE VERY WORST OF THE HUMAN SOUL.

Byline: Bob Strauss Daily News Film Critic

``Apt Pupil'' is creepy in ways you almost can't imagine. That's the source of its mesmerizing power; we know the unimaginable did happen, and this film shows us how easily it might again.

A shrewd, superbly acted adaptation of a Stephen King story, the movie is directed by the richly imaginative Bryan Singer of ``The Usual Suspects'' fame. In the broadest sense, ``Apt Pupil'' is a crackerjack mystery as well, only this one isn't a whodunit, it's a how-could-they-have-done-it.

The answer is so simple, it's absolutely chilling.

If Stephen King's great gift - other than making people jump when he writes ``Boo!'' - is his ability to evoke the horror lurking at the edge of middle American normalcy, this story has got to be his ultimate testament. Forgoing his usual supernatural trappings, King tried in ``Apt Pupil'' to examine the nature of evil in the human soul.

Singer does a better job of it by not trying, paradoxically, to get all psychological or trying very hard to come up with an explanation. Though major portions of the film are devoted to an old drunk and a teen-age boy talking, ``Apt Pupil'' is remarkably cinematic in the way that it shows man's worst impulses expressed in a dead-eyed glance or a subtle but triumphally cruel gesture.

Brad Renfro, the kid from ``The Client,'' plays Todd Bowden, a 16-year-old honors student in a pleasant, Southern California suburb who learns about the Holocaust in school and, well, wants to know more. After memorizing everything he can find at a nearby archive, Todd starts thinking an old man who rides the same bus with him looks oddly familiar.

Todd eventually confronts the elderly German gent in his ramshackle home with indisputable evidence that he's really Kurt Dussander, a concentration camp commandant who's been on the run for four decades (the film takes place in the mid-1980s). After a few feeble denials and empty threats, Dussander resigns himself to the inevitable end of a life defined by ingenious deception, paranoia and alcoholic loneliness.

But Todd has a different fate for Dussander in mind. Rather than turn the old Nazi in, he wants to hear his stories. All of them. In gory, sadistic detail.

Dussander initially balks, but the homespun Hitler Youth has power over him and knows how to apply it. Over the months, as the torrent of horror stories rolls, it starts affecting Todd's dreams, his grades and - most aptly - his attitude. When he passes a certain, inner point, woe befalls any weak or wounded creature that finds itself in Todd's path.

Meanwhile Dussander, played with a balance of cranky, malevolent brilliance and unnervingly avuncular charm by Ian McKellen, comes to realize that he's being revitalized as much as threatened by the boy. Having presumably suppressed his monstrous nature for 40 years, he sweetly surrenders to that awful, wonderful rush of power over others, and it pumps life back into his atrophied veins.

And nothing is more invigorating than calculating ways in which he can turn the tables and gain advantage over Todd.

Indeed, power is the blood bond that links these two moral vampires ever closer together, and Singer finds the true locus of evil in its magnetic lure. It's the movie's could-happen-here, or anywhere, thing; the fascistic promise of absolute control that flatters the insecurities of pubescent boys and impotent old men.

On the surface, at least, Singer and screenwriter Brandon Boyce have made a kinder, gentler movie about fascist pathology than the story King wrote. There is only one outright murder depicted and, somewhat amazingly, they've gotten the point across without resorting to a single anti-Semitic or racial slur. Some could, reasonably, call that a cop-out, the suggestion that evil can exist free of hatred.

But you can just as reasonably argue that that's how all of those good Germans found the madman's power fantasy so irresistible. At the close of this century of mass murder that also happens to be the century of cinema, ``Apt Pupil'' doesn't presume to tell us why the horror happened. But it gives us a shuddering look at just how, individual by individual, it could.

THE FACTS

The film: ``Apt Pupil'' (R; language, violence, nudity).

The stars: Ian McKellen, Brad Renfro, David Schwimmer, Elias Koteas.

Behind the scenes: Directed by Bryan Singer. Written by Brandon Boyce, based on Stephen King's novella. Produced by Singer, Jane Hamsher and Don Murphy. Released by TriStar Pictures.

Running time: One hour, 40 minutes.

Playing: Citywide.

Our rating: Four stars.

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Photo

Photo: A teen (Brad Renfro) fascinated with the Holocaust pumps an old Nazi (Ian McKellen) for the gruesome details in ``Apt Pupil.''