Someday, people may walk into an emergency room after a rape, or a car wreck, or a shooting, and be given a pill to protect them from the haunting memories that may follow.

For millions of war veterans, abuse victims and others, the psychological shock after a traumatic event can be as damaging as the event. Post-traumatic stress disorder, which affects an estimated 3 percent to 8 percent of the population, is typically treated with therapy to help the victim live with the memory.

But a researcher from Boston University will present research Friday that suggests doctors can keep a traumatic memory from being engraved vividly into the victim's mind in the first place. Instead of revisiting the victim as an intrusive flashback, the memory of trauma would be similar to recollections of ordinary events, fading gradually.

He and another researcher, working independently, are planning human trials to test their early findings that drugs commonly prescribed for hypertension could lessen the effects of post-traumatic stress disorder, or PTSD.

"It would have enormous public health relevance," said Dr. Glenn Saxe, the chairman of child and adolescent psychiatry at Boston Medical Center, who will present his findings Friday in Baltimore to the world's largest yearly meeting of traumatic stress specialists. If human trials confirm his observations, such drugs could be administered routinely in emergency rooms "not unlike [anti-clotting agents] are given to heart attack victims," he said.

Both Saxe and Dr. Roger Pitman, a professor of psychiatry at Harvard Medical School, believe that by dampening the body's adrenaline-fueled "fight-or-flight" reaction to great stress - and specifically by suppressing the neurotransmitter norepinephrine - they can prevent the vivid memories characteristic of PTSD. Saxe's human trials will test the long-term effect of the blood-pressure medication clonidine, which suppresses norepinephrine, on child and adult rape victims.

The theory has grown out of expanding knowledge of the process of memory creation.

Using drugs to help prevent PTSD, however, may not meet with universal enthusiasm among doctors who treat trauma. Although the terrorist attacks on Sept. 11 of last year have made PTSD an increasingly familiar diagnosis, much of its biology and physiology is still mysterious. It is unknown, for example, why one person recovers beautifully and another, who at first appears calmer, may be haunted for years.

For that reason, scientists should be cautious about affecting natural coping mechanisms, said one trauma specialist.

"I am someone who believes you have to do that really carefully, because if nature is giving us adrenaline at a time like this, there's a reason for it," said Rachel Yehuda, director of the Traumatic Stress Studies division at the Mount Sinai School of Medicine. "If medication delays your dealing with the event, maybe you'll pay for it later."

But others interviewed said the medications are a promising new direction. In both humans and animals, memory is heightened and enhanced by certain kinds of stress or fear. A group of college students tested by researchers at the University of California, Irvine, for example, could remember a series of slides better when they were accompanied by an upsetting or frightening story.

The best explanation for this hinges on the rush of stress hormones - including adrenaline and norepinephrine - whose release in the brain is triggered by fear, causing vision to improve, pupils to dilate, and the heart to pump harder. When they reach an area of the brain called the amygdala, known as the brain's "fear center," those hormones also enhance memory, which explains why years or even decades later, people can remember precisely where they were when they received catastrophic news.

"If you had a memory for every time you tied your shoe that was as strong as a memory for when you hear a loved one has died, you can see the importance of a built-in biological system that weighs memory storage according to importance," said Larry Cahill, an assistant professor of neurobiology and behavior at UC Irvine, who designed the study of college students' memory.

But enhanced memory, an evolutionary trait that served to teach our ancestors to avoid threatening situations in the future, may sometimes "overshoot . . . that system" to cause PTSD, said Pitman.

So the scientists decided to try blocking the stress reaction. Cahill took the group of students who saw the slides along with a disturbing narrative and gave them popranolol. This time, their memories were only as good as those of their non-frightened counterparts.

Meanwhile, in Boston, Pitman was doing a pilot study of 40 people recruited in the emergency room of Massachusetts General Hospital. A month after undergoing a 10-day course, none of eight subjects treated with popranolol had a stressful physical response to re-creations of the traumatic event, whereas six of 14 subjects treated with a placebo did.

Pitman said he and his colleagues are hoping to support their work with grants rather than pharmaceutical company money. Since the medications the researchers are using are no longer subject to patent, he said, there's "not going to be drug company money available."

But considering the cost of treating full-blown PTSD, and the substance abuse that goes along with it, any preventive measures will save money on a national scale, said Lisa Nijavits, director of the Trauma Research Project at McLean Hospital. "The ultimate question is what prevents human suffering," she said.