Why are horror movies popular year after year? I once asked George A. Romero, director of the classic ''Night of the Living Dead,'' and he said it might be for the same reason people live in regions with cold, hard winters.
Wes Craven, another scare specialist, also thinks macabre fantasies provide a way of staying in shape. They're a ''boot camp for the psyche,'' he told me recently. Young people especially like the genre, in his view, because they're in an unsettled time of life to begin with and - these days -feel the world is entering a shaky and even frightening period. A good horror film ''puts them under terrifying conditions and shows that you can survive. You come out feeling better and stronger.''
This doesn't go for all examples of the breed, of course. Craven himself says the unmitigated ''splatter'' movies are ''a terribly dark view to give a kid under any guise, including entertainment.''
But he feels there are redeeming values in his own new picture, ''A Nightmare on Elm Street,'' which features a strong and resourceful heroine as well as a despicable villain. Craven has indeed mellowed since his first feature, ''The Last House on the Left,'' a memorably loathsome chiller in which the teen-age heroes were all dead with a third of the picture left to go.
''A Nightmare on Elm Street'' is the second movie this year to locate its bad guys not behind a tree or under the bed, but in our very dreams. Like last summer's ''Dreamscape,'' it plays with different levels of illusion, blurring the boundary between what is and isn't real.
Since movies are rather like dreams anyway, this is a tantalizing premise. The climax even has a message: When the heroine beats the monster, it's by recognizing the unreality of the nightmare he comes from. This reflects Craven's idea that ''the only way to ultimately end violence is to turn away from it, to take its energy away.''
Not that ''Nightmare'' is easy to take. It has lots of the obligatory gore, and illustrates some of Craven's less optimistic opinions - that ''respectable'' middle-class people are capable of great violence, and that ''violence needs to be shown for what it is'' to counteract falsely upbeat notions of history and world affairs, not to mention the underside of human nature.
Even the triumphant climax is undercut by a last-minute switch, since Craven is suspicious of neat solutions. But the film is well crafted when some flat performances don't get in the way, and it's refreshing to see a young woman win a few in a horror picture for a change.
'Night of the Comet'
The heroines are winners in ''Night of the Comet,'' too. And that's just one surprise in the freshest and funniest science-fiction epic of the year.
The setting is Los Angeles, and the first villain is indeed a comet, which disintegrates the earthlings who watch it fly by - almost everybody, it turns out. The survivors are a few youngsters, zombies, and scientists, who stalk one another through the remaining reels.
It sounds like ordinary stuff, and it would be if not for the absurdist screenplay and deftly comic performances. The action centers on two teen-age sisters - one a resourceful type, the other a Valley Girl cheerleader, and both as strong and rugged as any male in sight. The end of the world fazes them a bit , but soon they make the best of things, combing stores for fashionable clothes and arguing over a cute lad who might be the last datable boy on the planet.
It's a modest production, with some dull spots and special effects so tacky they become a running gag. But it's light and lively most of the way, and as unpretentious as they come. In all, a real sleeper. Thom Eberhardt was the writer and director.
'Silent Night, Deadly Night'
Halloween horrors and chain-saw massacres are bad enough, but you just can't break the last taboo: Santa Claus. A new movie called ''Silent Night, Deadly Night'' dresses a psycho as St. Nick and puts an ax in his hands. Parents have protested in Chicago and New York, among other cities, prompting a curtailment of showings or a damper on advertising in some cases, according to the entertainment newspaper Variety.
Since the movie is pretty poor by any standard, and no more egregious than many other violent thrillers that the protesters have ignored, it would probably have faded quickly on its own - perhaps even faster than it will now, since controversy often helps at the box office. The most effective scenes come in the first half, as yuletide traumas turn a young boy's thoughts in nasty directions. The rest is a string of standard shock scenes, routinely churned out by director Charles Sellier Jr. and an uninspired cast.
The most frightening thing to ponder is where the Hollywood scaremongers will turn now that Christmas has joined Halloween and Friday the 13th as horror-movie holidays. Will next year bring ''The Arbor Day Murders'' and ''Dracula Meets the Easter Bunny''?