Moviemakers are bending over backwards to feed the apparently insatiable appetite of Americans for being scared out of their wits. But in the process of out-scarifying every other scary moviemaker, out-specialing everybody else's special effects, the flicks are getting to be a headache - or a seizure.

The problem isn't the horror-evoking phantasmagoria of the outer-space monsters in the currently popular science-fiction flicks.

It's just the flicks' flickers.

To possibly tens of thousands of migraine headache victims and a comparatively smaller number of epileptics, many of whom like to be scared-to-death as much as the next guy, the sinister-flicker syndrome is a real pain.

This season's popular outer-space thriller-chiller is "Alien," which does have a long scene in the final segments of the movie in which one of the besieged humans prowls a corridor of the spaceship while the deadly monster presumably lurks nearby. And while the Dolby system fills the theater with pulsating sound, stroboscopic onscreen lights are pulsing and pulsing and pulsing.

"Alien's" strobe scene - although there is no evidence that it is producing seizures or headaches in its audiences - does underscore the problem of the uniquitous flicker. In fact, strobe frequencies are often used in the diagnosis of brain disorders as in epilepsy or migraine. It sometimes can make the brain waves "go bananas," on an electroencephalograph (EEG) said Dr. Joel Saper, chief of the University of Michigan Headache Clinic in Ann Arbor.

According to headache specialists, strobe-sensitive migraine victims can have their headaches triggered by such mundane things as:

The flicke of a fluorescent light about to go out.

Sunlight glimmering through trees.

Changing the TV channel.

A disco.

Motion pictures and TV programs with flickering lights or vividly contrasting scenes.

The same things can provoke seizures among those epileptics sensitive to flashing lights. And although the flicker-sensitive are relatively few in numbers, the Epilleptic Foundation is aware of the problem and is wrestling with ways to help its clientele cope.

Peter Van Haverbeke of the Epileptic Foundation here said that most recently the foundation heard from a woman has whose seizure was triggered by a current TV commercial.

That is not uncommon phenomenon with which the specialists are familiar, he said, noting that a recent transmission problem in England had produced a rash of seizures there. (Note: That particular transmission problem, he said, is a product of the European TV system which is different from that used in this country.)

Moviedom is not totally unaware of the phenomenon either. The plot of the film "The Andromeda Strain" turned on a woman scientist's seizure that was set off by a flashing alarm light!

Dr. Saper, who is the author of the recent book "Freedom From Headaches," noted that the brain waves of epileptics and migraine patients share a sensitivity to the sort of stimulation flashing lights provide, and it is not at all surprising that the same flickers that produce the seizure in one will provoke the headache in another.

A similiar phenomenon has been noted by Dr. Seymour Diamond, director of the Diamond Headache Clinic in Chicago, who confirmed that his patients do sometimes complain that a headache was triggered by a motion picture or television program.

Van Haverbeke said that the Epileptic Foundation had actually tried to devise some guidelines for television and motion picture producers to use in terms of visual effects that could provoke seizures but he said, that has not proved posssible. The problem is the vast range of sensitivity. One patient might have a seizure (or headache) when confronted with only a few flickers a second for only a few seconds at a time. Others might not be bothered by 100 flashes a second. Then too, other factors such as fatigue, weather, atmospheric pressure or humidity can heighten or lessen sensitivity in an individual from day to day. In general, though, the longer the flickering lasts, the more likely it is to cause disturbance. (The "Alien scene "seems to go on forever," said a viewer who, however, conceded that the suspense factor may have stretched the minutes. It lasts several minutes.)

There doesn't seem to be much hope of eliminating the flicker from the environment, so until the headache specialists find the answers they admit do not come easily, the flicker-senstitives need to take their own precautions.

A spokesman for Twentieth Century-Fox, whihaded or tinted glasses are a help. Some physicians treating epileptics suggest that TV should be watched in a lighted room to lessen the contrast, or even that someone other than the susceptible person change the channels.

A spokesman for Twentieth Century-Fox, whi ch released "Alien," said yesterday he hadn't heard about the film causing any headaches or seizures, but he added gleefully, "We've heard of people who couldn't take it."

If you want to see "Alien," and you're worried about the strobe, you can always bury your face in your hands. You'll just look terrified. And after all, that's what you're supposed to be.