IT KEEPS happening all over Washington. A Takoma Park woman peeks into the sack of bluefish filets her husband has hauled home from the bay and for a hideous glinting instant...Alien. Or something as innocent as bean sprouts bursting out of dirt in fast-motion film on Sesame Street raises goosebumps...or a cat-gnawed rat head on the porch, fangs arching....

Dan O'Bannon unzips the fly of his Levis for comfort, then sits crosslegged in the chair in his hotel room.O'Bannon is the screenwriter and concept man behind this year's biggest terror flick, "Alien." It's about a spaceship terrorized by a monster whose hideousness, say a lot of fans and critics, goes far beyond that in any previous horror movie.

O'Bannon is here as featured guest of a science fiction convention.

He nuzzles a glass of Perrier water and sucks on a Pall Mall with small watchful gestures. His lips part with his flinch of a smile. He seems pleased to learn that long after the movie his monster keeps writhing away in malignant afterflashes.

"I wanted to raise movie monsters to a new level. I wanted to introduce a new demon into public consciousness, " and I wanted to speak directly to the unconscious. That demon in "The Exorcist" was just funhouse evil. I very definitely wanted the audience to have a feeling of extraordinary primal evil, which is why I made it a sexual caranivore."

Carnivorous, certainly, but sexual?

O'Bannon's face shifts into a wondrous stare, wide-eyed and deadtired at the same time.

"Of course. It uses its victims as a host. It rapes them. Then they give birth. This is what makes it so disturbing."$&(WORD ILLEGIBLE $&)See O'BANNON, £8, Col. 5> $&(WORD ILLEGIBLE $&)O'BANNON, From £1>

So disturbing. "After the sneak previews, the studio executives were worried that people weren't screaming enough. They said they were giggling. So I went and looked for myself and I saw they were giggling with fear."

And talking out loud and striding back to the bathrooms and smoking cigarettes in the lobby, if one recent showing is a fair example. Becasue evil, in the 20th century, is supposedly banished into history, a figment of superstitious imagination, at worst a failure of behavioral conditioning. Or just a moviemaker's trick. Wouldn't it be lovely to think so?

But O'Bannon meant the movie as an "attack" on the audience; he wanted to "get even," he says, for the way they scorned him for his first movie, "Dark Star." He wanted to "beat the stuffing" out of us, he says. He means it.

O'Bannon sleeps with a loaded pistol by his bed. He never walks down a street without fearing assault. He's even developed a special defensive walk. "You want to see it?" He stands, zips up his pants and sidles across the hotel room as if he were shrugging through one beaded curtain after another. He seems to focus his eyes somewhere in the middle of his own head.

"I never make eye contact with anyone. I assume a fixed expression that says "don't bother me." "

His lank blond hair sways, his shoulders hunch. He wears a beard with no moustache. He is small, vaporous, a drift of bitter protoplasm back toward the chair where he unzips his fly and sits down again....

"All through my childhood and my teens I was constantly picked on, attacked, assaulted. I abhor violence. I don't think I could portray it if I didn't abhor it so much," he says in a flat, dead baritone.

"I grew up in a small town in Missouri named Winona, a dreadful place. We moved to St. Louis during my adolescence. That was even worse. If I had my finger on the button, the first place I'd blow up would be St. Louis. The whole medium of social interaction in St. Louis is games of humiliation. The ambience is depression, despair. For me the world is shaped like a funnel and St. Louis is at the bottom. It's a fight to keep out of it.

"I was an only child. My father was a carpenter with an IQ in the genius range. He was multi-talented in the arts, but he'd grown up too poor to be able to exress himself. He always put people ahead of principles, but my mother was the reverse. She was phychically violent. She'd throw me to the wolves for a principle."

He attended four colleges, the last being the University of Southern California, where he studied film. He hitchhiked around the country, did a lot of drugs, and in 1969, at the age of 23, began a science fiction movie called "Dark Star," a comedy. It took 3 1/2 years. It flopped, breeding the rage in which he soon afterwards began writing "Alien," which has occupied his last four years.

"Sure, comedy. I could always make people laugh, in high school. Then I began to discover that people were laughing at me rather than with me. I got angry. That anger has accelerated. I used to make a lot of jokes, I could stand up on a stage and make people laugh. But I mistook the laughing for people liking me, and I began to get angry.

"The great turning point was 10th grade, I'll never forget it. I was sitting at a play rehearsal, and I asked an upperclassman why I didn't have more friends. He said, "If people don't like me, - 'em." That's when it began. I went home to think about that. - 'em."

He was an extrovert, he says. Now he's a loner. "I wanted to go to all the parties. But I got rejected and rejected and rejected. Girls always considered me creepy. But I'm used to being alone now. Of all the areas of my life, the most terrible with the least success has been with women. When I was a kid, I wanted to get - so bad, I was such a horny kid. In my 20s, I grew up a little and I wanted a stable relationship with one lady. It didn't work. I see other people happy in relationships, and I'm such an envious person...I hadn't had a baker's dozen of women until I was 28. Then I got money, when we started working on "Alien." Since then, I must have had 300 women. brains out."

Exactly what difference did the money make?

O'Brannon's face flinches back into tired wonder again. "Prostitutes!" he says. "I've learned that if you don't pay for sex with money, you pay for it with psychodrama. All women want somethin in return for sex. I've learned too that women who just want sex are dangerously insane."

Given the conventional psychotherapeutic morality play of our times, O'Bannon should have turned into a dangerous criminal instead of this brooding seether.

"I can't be violent. It's not in me. Once, in gym class, some jerk rushed up and threw after-shave lotion in my eyes. They burned, they hurt, I was full of shock, and rage - rage so great that I felt no fear, for once. I chased him, I saw fear appear in his face. I slammed him against a locker and I drew back my hand to smite him, but some invisible force held my hand.

"As you may know, the beating of women is common in this country. At the end of [one] relationship, I felt very abused, rejected and manipulated. She said a bunch of things that were so hurtful I can't even repeat them. I turned to her, out in her garden. She had a gun, a .22 Colt varmint pistol. She said: "I'll use it." I wanted to kill her. I knocked the gun out of her hand and gave her a shove but it was like shoving cellophane. I thought; "My God, this person is so weak." So I turned and began to beat myself in the head with my own fists."

The list of assaults, wrongs and contumelies goes on and on. When "Dark Star" opened, O'Bannon and his director went to a theater, introduced themselves to the manager and said they wanted to watch audience reaction. "The manager said: "What audience? There's eight people in there." "Dark Star" is a trauma from which I have yet to recover."

So was it satisfying when he heard those first "Alien" audiences gibber with fear?

O'Bannon leans forward, the rims of his eyes spreading very tense, his lips flattening against his teeth. "Yeahhhhh!" he says. "I wanted to get even. And by God, it worked."

O'Bannon wrote the script "unisex," he says, leaving it to the director and re-writers of the script to decide which of the characters would be male, and which female. They, not he, selected a woman, played by Sigourney Weaver, to be the last person to face the monster. That was fine with him.

"Having her peeling off those clothes...that soft certainly makes her vulnerable, doesn't it?"

So he's rich. Famous. Vindicated. If it weren't for his stomach attacks, he might get his first shot at happiness; but they started coming on during the last year of work in the movie, incredible gut pain and nausea that the doctors, after endless scans and probes, found no cause for, whatsoever. The only cure is to shoot him full of Demerol and feed him intravenously. He just got out of the hospital a few weeks ago after one bout, but his worst attack came during the sneak-previews - one of the preview cities being his hometown of St. Louis, ironically enough.

The movie was not easily made. It grew from a low-budget thriller to a big-budget studio production, frantic searches for designers and a director who could convey the eldritch grisliness O'Brannon had dredged from the id-muck. At the end, two other writers who had worked on the script after him tried to bump him from the credits, a fight that he won in union arbitration.

"Actually, I got more credit in the end than I deserved," he says, shrugging at the irony of vengeance.

'Bannon has no hobbies, no relaxations to speak of. He's still so numb from working so hard he can't savor any of his success. He has to think for a while before he can think of what he does purely for fun.

"Sometimes," he says, brightening, "I like to get totally stoned out of my mind. Liquor, marijuana, everything. Just get completely stoned, and go to some sleazy strip joint and spend all night watching the girls dance." CAPTION: Picture, Dan O'Bannon, who dredged the story of "Alien" out of the turmoil of his life. By Joel Richardson - The Washington Post.