For Brian Hanis, the Monday afternoon it happened was no different from a dozen other school days.

The sophomore basketball player decided to skip his team's weightlifting exercises and head home. He caught the bus from his school in Sherman Oaks and got off near his family's apartment complex in Woodland Hills. As usual, he listened to his Walkman for the short walk from the bus stop to his front door.Brian went straight to his bedroom and called a friend. Just as he said goodbye, he was startled by a stranger standing in the doorway of his room and aiming a gun in his direction.

"I think I sort of screamed," Brian said. "He took two steps toward me and told me to hang up the phone. Then he asked me for money."

The student told him he had no money. The intruder instructed Brian to lie face down on the bed with a pillow over his head while he searched the apartment. Brian obeyed but first made a mental note of the time: 4:33.

"I thought, `This is it,' that I wouldn't play my first basketball game and wouldn't get to listen to rap music anymore," Brian said. "Then I thought about Lori."

His 12-year-old sister was due home from school any minute. She was the reason he left the front door unlocked.

But the robber was gone when Lori walked in at 4:55.

For the next few days, the children and their mother, Kathy Hanis, were overwhelmed by feelings of anxiety, panic, helplessness, guilt and anger. Brian was nervous, couldn't sleep and kept wondering why he decided to ditch weightlifting that day. Lori refused to sleep in her room or go near a window and insisted they move to a new home.

The children's symptoms were fairly typical after experiencing such an ordeal, psychologists say. If they are given the opportunity to talk about the incident and are assured that their feelings are normal, most children conquer their fears and regain their composure within a few weeks. But if those signs persist or the youngsters exhibit new symptoms, they may need professional counseling.

"Not all children who are victims are traumatized," said Spencer Eth, co-author of "Post Traumatic Stress Disorder in Children and Adolescents" and acting chief of psychiatry at the Veterans Administration Medical Center in West Los Angeles.

"Parents should be alert to anything (symptoms) that lasts more than two weeks or behavior that interferes with everyday functions," Eth explained. Such conduct in a child could signal post-traumatic stress disorder, a psychological term that describes the inability to cope with one's emotions following a shocking occurrence.

When a child experiences an event that is life-threatening, his sense of security is greatly diminished, said Thomas Hicklin, assistant professor of psychiatry and behavioral science at USC.

"A child and an adult go through similar feelings (following a trauma), but the child has not yet developed the same coping mechanisms," he said.

Post-traumatic stress disorder can be initiated by being a victim or witness to assaults, traffic accidents or kidnappings; involvement in natural catastrophes such as floods and earthquakes; experiencing the death of a loved one or peer; and even being denied entrance to a favored college, psychologists say.

"The worst thing a parent can do is minimize the event in an effort to be reassuring," said Susan Stone, clinical director of the Santa Clarita Valley Special Children's Clinic, who warns against telling a child to "shape up" or calling him a baby. "Such an attitude conveys to the child that their feelings are not normal."

When a child survives a one-time trauma, such as armed robbery, he tends to focus all his emotional energy on that one event immediately, she said. He may feel angry that his parents weren't there to protect him and overwhelmed that he can no longer control his world. A witness or survivor, meanwhile, might feel guilty about being spared.

"During the incident, children will often block out all feelings and distance themselves from their bodies," said Linda Damon, clinical director of child-abuse services at the San Fernando Valley Child Guidance Clinic. It's the same sort of reaction exhibited by a child who is exposed to chronic trauma, such as child abuse. But that's where the similarities end.

The one-time sufferers will show obvious signs of fear afterward and think about the trauma obsessively. A young child may re-enact the incident while playing or draw it on a piece of paper. An older child will talk or daydream about it.

Children who endure ongoing trauma build defense techniques in order to cope; they disassociate themselves and become void of emotions, Damon said. "It's like they're wearing their armor even when they're not in battle."

But even victims of one-time trauma can carry psychological scars as deep as those of constantly abused children, especially when that single episode was extremely intense, said Dr. Barbara Ferguson, director of the Child Study Center at St. John's Hospital in Santa Monica, Calif.

She cites the mental conditions of some of the children from the 1976 Chowchilla school bus kidnapping as an example. After being buried underground in a truck trailer for 15 hours, one child's distorted image of his surroundings after emerging from the giant hole was that of an idyllic country landscape. In reality, the location was "a very desertlike environment," Ferguson said.

Crucial to a child's emotional healing following a traumatic event are the actions and attitudes of parents and teachers. Often, adult family members are so overwhelmed themselves that they neglect the special emotional needs of the children, said Pete Getoff, case-work supervisor and licensed clinical social worker for El Nido Services, a non-profit child and family service agency with 16 offices in the Los Angeles area.

"When a child is traumatized, typically the adult is also," he said. "If the parent decides the way to cope is to shut out the event, then he won't take his child in for help because it means he has to face the trauma all over again."

A recently arrived family from El Salvador, for instance, may attempt to forget their ordeals in that war-torn country by not discussing them, but the children may still have vivid memories they need to talk about.

Such situations are occasionally encountered by Loeb Aronin, director of psychological services for the Los Angeles Unified School District.

"Sometimes there are cultural differences that must be noted before treatment can be effective," he said, explaining that some ethnic groups view counseling as a shameful admittance of one's weaknesses.

The L.A. school district has a staff of psychologists who rotate from school to school, Aronin said. Most teachers are aware of the symptoms that indicate a child may be under stress or trauma and should be trained to handle the situations with sensitivity. Sometimes an event can traumatize the entire student body, as in the case of snipers terrorizing schools in Los Angeles and suburban Chicago, and the death of teacher Christa McAuliffe in the Challenger space shuttle accident.

Aronin and the other psychologists agree that Brian's mother did the proper thing by notifying school officials and her priest of the robbery.

"The key is helping the child feel in control again, and the process is helped along when everyone in an intervention capacity is made aware of the crisis," he said.

"I knew it meant another adjustment period, just when we were starting to feel comfortable about our surroundings," said Hanis, who moved her family from Kansas City, Mo., in August, two months before the robbery.

Brian said he worked through his initial fears by talking to an uncle who is an FBI agent, and to the priest.

"For the first couple of days, I could hear his (the intruder's) voice and see him, like he was still here," Brian said. "Now I just look around everywhere to see who's around me."

Lori couldn't convince her mother to move, but did talk her into switching bedrooms.

"I could see his footprints in the carpet and knew exactly where he stood in my room," she said. "It was creepy."

Now the family has become more conscientious about locking doors and keeping tabs on each other's whereabouts.

"Thank heaven it wasn't worse," Hanis said.

*Following a traumatic event, a child may show symptoms of post-traumatic stress disorder. These symptoms may include:

-Nightmares and sleeplessness.

-Regressive behavior, such as thumb-sucking and bed-wetting in young children.

-Vague physical problems, such as stomachaches or cramps.

-Loss of appetite.

-Misbehavior or aggression not there before the trauma-inducing event.

-Flashbacks or distortion of the event.

-Survivor's guilt.

-Anxiety about being alone or separated from familiar people or places.

-Change in attitude at school or poor grades. Trouble concentrating.

-Excessive chattiness or sudden quietness.

- As a parent, guardian or friend of a child who has faced a traumatic event, psychologists suggest these tactics for helping him through:

-Encourage the child to talk about the incident. If the child is very young, he may need to draw it or act it out. If he doesn't want to talk about it, encourage him to write his thoughts down in a journal or letter. Psychologists say these are all ways of helping the child feel in control again. However, if the child become too obsessive, they advise that parents seek professional therapy.

-Talk about how he can avoid the experience in the future. "Help him make sense of `Why me?"' said Linda Damon of the San Fernando Valley Child Guidance Clinic.

-Find ways to make the child feel safer. Perhaps a new lock on the door or a key chain with a loud whistle will make him feel more secure against strangers. If he's fearful of coming home to an empty house, send him to a caretaker's or friend's home. Put together an earthquake kit and practice preparedness drills to alleviate his fear of not surviving.

-Don't forget about siblings and friends who may not have been witnesses but could feel they narrowly missed being hurt. In some cases, children feel a survivor's guilt - they may even feel bad about feeling lucky that they weren't the victims.