Grab your hats, O observers of American culture. Here's a streamlined chance to see what subtleties the last quarter-century has wrought. Banking on the new "Invasion of the Body Snatchers" success, K-B Fine Arts is showing the original 1956 version. Seeing both is the cinematic equivalent of putting a '56 Chevy Belair next to a '78 Chevette: They both run on the same principle, but they sure look different. From that difference we can learn something about ourselves.

Both films center around an insidious alien-takeover plot. Emotionless duplicates of humans burst from pods while the victims sleep. Pod people populate the town in an omnipotent conspiracy that threatens to destroy humanity. One man and woman try to stop it, and although there's a different twist to the endings, the message is the same: There is no stopping them and you're next.

Like a 30-year demographic chart, the locale moves from an apple-pie American small town whose filling turns rotten with paranoia to teeming San Francisco where Craziness and paranoia are basic modus operandi. Fresh-faced, slick-haired Kevin McCarthy plays the original Miles Bennell, the local doc who knows everyone in town and watches them change. He and former high-school sweetheart Becky Driscoll, played by Dana Wynter, make copy references to Reno. This means they've both divorced spouses and can resume their affair. She lives with her father until he turns pod.

Thirty-two years later, the update finds a droopy, frazzled-haired Matthew Bennell (Donald Sutherland) as an alienated health-department bureaucrat who takes up with co-worker Elizabeth Driscoll (Brooke Adams) when her live-in lover becomes one of them.

Viewing the older version makes it plain that the update coats a '50s plot in '70s trappings. It still works, but the original comes across as a more compact, unified package. "So much has been discovered these past few years that anything can happen," says anti-pod protagonist McCarthy. Indeed. Atomic weapons, Sputnik, air raids and the communist threat had folks terrified. The porch swings and front lawns became a sham. Things were changing in a big way, and people were powerless to stop it. America's fall from innocence is depicted here as a kind of Father Knows Best Goes Bonkers. But by 1978, we've been in purgatory so long that Armageddon comes as no surprise.

Understatement prevails in the '56 version, and its fans claim that less is more. For others, all the '50s kitsch makes the film campy in a "Reefer Madness" way. Because of all the bulbous autos, chromey appliances and pointed push-up ladies' wear one can view from a safe distance. It's easy to watch weird things happen in black-and-white to a martini-sipping '50s type in a mink stole, but the same things happening in living color -- and Dolby sound -- to a beansprout-chewing '70s type in a caftan is a little more threatening. The '78 version also gets more gore mileage out of the pod motif, with horror for horror's sake. Although the original is more finely honed than its scion, it's a period piece. Chill for thrill, the new "Body Snatchers" is the scarier picture.But the real chill is in seeing both and drawing your own cultural conclusions.