High-Risk Love in an Alien World SOMEONE TO WATCH OVER ME Directed by Ridley Scott Screenplay by Howard Franklin

By RICHARD CORLISS

The stark fantasy goes like this: New York City is two different, alien worlds: Manhattan and the "outer boroughs." Manhattan, America's hub of service and information, is an island where the rich get richer and the poor serve lunch. Each day the sunrise set emerges from its Manhattan high-rises, takes a limo to the office and sits down to run the computer age. At the same hour, folks come in from Brooklyn or Queens to play the worker-bee roles of secretaries, cab drivers, souvlaki vendors and cops. After work they return home in underground cattle cars. The subway straps might be handcuffs.

There is a catch for the powerful though. No matter how upscale a Manhattanite climbs, he can never escape the sight of poverty or the threat of violence. The glitterati on their way to a $1,000-a-ticket gala must tiptoe through the homeless camped outside in their cardboard condos. And at this week's chic disco -- in this week's beyond-chic movie thriller -- a wealthy young woman named Claire Gregory (Mimi Rogers) may be witness to a murder. And be tabbed and stalked by the killer. And be protected by Mike Keegan (Tom Berenger), a Queens policeman who knows no more of haut-monde Manhattan then he may have seen on Lifestyles of the Rich and Famous.

At first Mike lounges warily in Claire's palatial digs, tossing newspaper wads into the sconces. Mike considers her with the outsider's mixture of scorn and awe. But why should he consider her at all? He is at ease in the world outside Manhattan; he has a loving wife (Lorraine Bracco) and a fine young son. For that matter, why should Claire think of Mike as anything but a nuisance or a clown? He shadows her everywhere, mangles the language and dresses like a used-car salesman at Sunday Mass. Yet she responds to his strength. Though she has a rich man to provide for her, she needs a protector. Perhaps she needs a lover. And Mike surely needs danger.

Someone to Watch Over Me is Ridley Scott's first contemporary film. But the director of Alien knows about hostile environments; the director of Blade Runner knows how to mix sleaze and sleek; the director of Legend knows about the perils of passion. Scott is also an ace stylist, and set loose in New York City he creates a Deluxe color version of an Old Hollywood vision: Manhattan in the '40s, with its twin thrills of grandeur and menace. The sidewalks gleam like a Bakelite floor. A hired gun jogs into a Fifth Avenue foyer.

For all its tech-noir gloss, this is still a traditional thriller, eager to deliver moral lessons with its frissons. Cheat on your wife, and maybe she gets hurt. Leave your family, and maybe they get kidnaped. Go to bed with a woman you work with, and maybe she dies. These are New Hollywood's scary metaphors for sex in the high-risk '80s. Last year The Fly said that a woman could get involved with a nice guy who metamorphoses into a slavering insect. The current hit Fatal Attraction preaches that no man is safe from a fling who gets flung: her jealousy cuts like a knife. Scott's film, cooler, less apocalyptic, says only this: Know your place -- Manhattan or Queens, restlessness or security -- and stay in it. Alien worlds should never collide.