TWO YEARS ago, after spending most of her adult life in London, my younger sister moved to the Hardyesque peace of a Dorset village. She now spends her days surrounded by cows and trees and is, by all accounts, blissfully happy.

Last week she came to London for a few days and was shocked by its crudeness. Some specific examples: the commercials she watched before seeing the film Howards End. One featured two youths with greedy faces, bloated with material possessions, but presumably intended to epitomise young male desirability. Another showed people dancing with an explicit sexuality that repelled her. There was no subtlety or irony in these commercials; the clear assumption was that today's audiences admire behaviour that is ruthless and strident.

Real life bore this out. She found the language of young women markedly more obscene; nor was it just their language . . . couples were French-kissing and groping one another publicly after a few drinks. In the short time she has been away, the behaviour of women in particular seems to have become defiantly and blatantly sexual. My sister (believe me) is not a prude. I know that decorum has long since gone; what worries me more is the apparent lack of tenderness in these encounters.

I was curious to find some parallel of my own to her experience, so on Saturday I went to a film I would not normally have chosen to see: a science-fiction horror movie. I have led a sheltered cinematic life. My closest encounter with such films has been The Company of Wolves and ET. But I was assured that the special effects in Alien3 were marvellous, and that it would be absolutely terrifying. I prepared for marvels and terror.

Over the opening titles the audience is teased with micro- second images of something larval . . . skeletal . . . rapid yet slimy; something that touches on our most primitive fears. These images are superimposed on the face of a sleeping woman, backlit so as to emphasise the soft, vulnerable texture of her skin. This juxtaposition states the threat from the outset. It comes from something hidden and visceral, to menace all that is comforting and familiar.

The action - and when the hype's said and done, this is just a 'search and destroy' movie - is set in a bleak, anonymous environment, like a Siberian prison camp. The whole film could have been shot in black and white, so drained of colour is it . . . except, of course, that then you could not recoil from the gleaming dark red blood that seeps and flows and splashes across so many scenes.

Yes, the special effects are well done; yes, the film has exciting moments. With a woman as heroine (although I gather the approved word is now 'hero', whatever the sex), leader, avenger, nurturer and sacrifice, Alien3 has pretensions to political correctness.

Sigourney Weaver as Lieutenant Ripley is - believe it or not - shorn of every feminine attribute except for the shifting glimpsed occasionally below her loose grey T-shirt and an unquenchable maternal instinct. The film even offers a message of hope and redemption from the lowest depths (most of the characters are multiple murderers, rapists, etc), reinforced by blasts of organ music and heavenly choruses to ram home this portentousness.

What interested me was why this concoction of simplistic moralising, feminist ideology and larval as well as human brutality should have world-wide appeal? Twentieth Century-Fox has spent (it is said) more than dollars 50m ( pounds 26m) on a film whose sets go from abattoir, prison and sewer to the usual futuristic bank of computer terminals.

Why do audiences today want all this? Is it because the film portrays an environment so bleak and ugly that even the most nihilistic unemployed person from ghetto or housing estate can feel 'At least I'm better off than that'? Or does it cater to masochism and self-hatred?

I found most disquieting the fact that Sigourney Weaver is stripped of all beauty and tenderness, changed into a being as violent and foul-mouthed as the convicts among whom she lands and portrayed as a dangerous, contaminating force - because in spite of everything she is a woman. Alien3 expresses fear and hatred of women, despite its espousal of the apparently correct feminist line.

I am no habituee of this film genre, and so I found its subtext difficult to interpret. The simplest conclusion is that audiences enjoy being nauseated and horrified - including the affluent audience in whose midst I watched it. The certainty that Alien3 will be avidly consumed by millions alarms me very much indeed.