LOS ANGELES (AP) _ In suburban Garden Grove, three gun-wielding gangsters force their way into an apartment, hogtie and savagely rape two women and rob them of $500 and some jewelry.

Nearby, in Yorba Linda, another armed band smashes through the glass door of a family's home, binding and robbing six people, including the grandparents, during a six-hour reign of terror. When the grandfather asks them not to take his watch, they shoot him in the leg.

In both cases, the victims were Vietnamese - but so were their assailants. Throughout the country, police say, Asian gangs are targeting their own, committing violent ''home invasion robberies'' against Asian families and extorting money from Asian businesses.

And the police rarely hear about it. The gang members stalk their victims, beating and scaring them to ensure that the crimes go unreported. Cultural wariness also keeps many Asian victims - especially Vietnamese - from reporting crimes to police.

Then, when detectives finally do get leads, they're up against highly mobile and very intelligent street gangs of 19- to 24-year-olds.

''Asian gangs tend to prey on their own more so than other groups,'' said Los Angeles County Sheriff's Detective Frank Gutierrez, whose substation in the heavily Asian central San Gabriel Valley typically handles about 10 to 15 home invasion robberies a month.

For most police, the area of Asian-on-Asian crime is unfamiliar terrain: Police don't speak the languages or understand the culture, let alone the brutal nature of the crimes.

In more than half of the residential robberies in which women are present, there is some type of sexual assault, says Philip Hannum, the co-founder of the International Association of Asian Crime Investigators.

''They'll (the robbers) sit and eat all the victim's food, drink all their alcohol and wait for the whole family to come home, one by one, and then rob each one of them,'' said Orange County Deputy District Attorney John Anderson.

''It is not uncommon for them (the robbers) to be in the home for hours. During the whole time the victims are tied up on the floor. They can't even look at the robbers or they get belted.''

In the last 18 months, Asian home invasion robberies have been reported in New York City, Sacramento, Seattle, Boston and Washington, D.C., among others.

Few police departments keep separate statistics for such robberies or other types of Asian-on-Asian crime. But interviews with Asian crime specialists suggest the crimes are pervasive.

According to Hannum, in the suburbs of Boston during the first three months of 1992, there were more than 20 unsolved Asian home invasion robberies. In the Houston area, in the last quarter of the same year, there were 34.

Speaking through an interpreter, a 43-year-old Vietnamese man from Garden Grove, Calif., smokes a cigarette nervously as he recounts the night a gun was put to his head and he and his wife were tied up during an invasion robbery - the first of two at their home.

''I still think about it. They might come back again,'' said the man, an unemployed television repairman who spoke on condition of anonymity. ''Maybe next year I'll move. I'm scared.''

Gang members knocked on his front door. He was suspicious and didn't open it. They returned three hours later, though, at midnight, and broke down the back door. After shouting at him and waving a gun, they took a camera, camcorder, Nintendo game set, the family car and $2,500.

As with most invasion robberies, this one began with an inside tip, police say. One of the intruders was the son of a friend of the victims who had scouted out the house during previous visits.

Police say the inside information may come from someone as close as a family member, girlfriend or boyfriend, classmate or colleague. It also may come from a source halfway across the country.

It's not unusual for a Vietnamese gang to commit a robbery in Los Angeles one day, fly to Texas for another one the next day and then be back in Los Angeles the day after that.

For the last 10 years, Thien Cao, a community service officer with the Garden Grove Police Department, has been working with Vietnamese victims, trying to coax them into being more comfortable with police.

It doesn't help, Cao said, that Vietnamese victims have trouble understanding the American bail system - gang members being in jail one day and out on the street the next.

In the Vietnamese community, Cao said, the leeriness toward police reaches back to Vietnam, where, he said, police are not accountable to anyone.

''Victims are more willing to go forward now, but the number is still small. The process is still very slow,'' said Cao. ''Usually when we find out, it's only after the fact. The victim calls their friend and then the friend calls the police.''

The gangs do not limit their activities to invasion robberies, of course.

Over 10 years, a Vietnamese couple in the Orange County community of Garden Grove saved up enough money to open their own business. But for the past six months, they say, gang members have been running up $100 unpaid tabs and stealing and beating other customers. When asked to pay, the couple says, the gang members threatened to burn the place down.

Once, said the wife, gangsters demanded $600 for a funeral for one of their members who had been killed in a shootout in Long Beach.

''Whenever I see them, I'm so scared I'm unable to cook,'' said the wife. Her 15-year-old daughter speaks the best English and usually works the counter after school. But, the mother says, the daughter has not been coming to work lately. She is too afraid.

Asked whether the presence of gang members has affected business, the wife sweeps her hand in the direction of the empty tables: The restaurant is without a single customer at lunch hour.

The restaurant is in a strip mall with nine other shops, including a beauty salon, a video rental store and a supermarket. All are owned by Asians, with the exception of one, an air-brush rental shop.

It is the only store in the complex that the gang members do not extort.