The legacy of the Vietnam war continues to hover over refugees in the United States.
One result: crime in the Vietnamese community that is sometimes political in nature.
The same youth gangs and secret criminal associations that developed among earlier immigrants are also found among Vietnamese. But observers both within and outside the refugee community say grudges and competing factions left over from the war also play a part.
The offenses getting attention include:
* Killings and assaults, both by gangs and individuals. Sometimes these seem aimed to settle political ''scores'' growing out of the war. But law-enforcement officials add that more usual criminal practices may also be involved.
* Extortionists pressing Vietnamese shopkeepers for ''taxes'' said to support anticommunist resistance groups in Vietnam. Just how much of this money actually goes to resistance groups is uncertain.
Some experts stress the need to avoid exaggerating the amount of crime among some 400,000 Vietnamese refugees who have arrived in the United States since 1975. Some Vietnamese say publicity on the subject may spread a misleading stereotype.
The issue has gained most attention on the West Coast, where there have been at least 10 gang or faction related murders of Vietnamese in the last 12 months. So far, these crimes have been reported in San Francisco, Los Angeles, San Jose, Garden Grove, Santa Ana, and Torrey Pines Beach.
Douglas Pike, a former US-government Vietnam expert, now editor of ''Indochina Chronology'' at the University of California, Berkeley, says that among the Vietnamese community in the US today, there are some 90 factional groups organized around leading personalities, much as in South Vietnam under President Thieu. Loyalty to persons can be as important as ideological issues, and individuals from time to time change loyalties from one faction to another. Thus grudges expressed in political ideological terms may conceal personal, factional frictions.
One obstacle to sorting all this out is the reluctance of refugees to talk publicly. This may be partly out of concern that publicity will give Vietnamese a bad name and partly out of fear of retaliation, observers say. Influenced by their experience in Indochina, refugees often conclude that they must solve their problems privately because police and courts are foreign groups unworthy of trust.
Law-enforcement sources have suggested that some assaults are committed by extortion gangs who ''shake down'' their Vietnamese victims to gain ''donations'' for the anticommunist cause.
Others, like San Jose State Anthropology Prof. James Freeman say the violence sometimes comes from loosely organized youth gangs who initially organize ''defensively'' against intimidation by other gangs of immigrants or established Americans.
This explanation follows the familiar pattern of earlier Irish and Italian immigrants. It also dovetails with the experience of youth gangs formed in New York City's Chinatown by immigrants from Hong Kong, who initially sought defense against Italian youth gangs.
''There is a spillover from the war in the way some groups organize,'' notes Professor Freeman, who is conducting an oral history project among Vietnamese. He adds it is difficult to know just how important this influence is because Vietnamese refugees are reluctant to talk to discuss it with outsiders.
''There is a potential for a great deal of violence by youth organizations, '' explains Freeman. ''I expect that unless headed off, this will grow.''
Among the measures he suggests are steps to reduce the expectation by young Vietnamese of hostility from outsiders. This might include Vietnamese language training for social workers, and better ''community relations'' contact between Vietnamese and police. One important goal, he says, is to prevent an anti-Vietnamese backlash, which could convince refugees they must organize to defend themselves.
In the case of extortion and related violence, the echoes of the Vietnam war appear very real. ''Some crimes may be committed by former ARVN (South Vietnamese Army) types who collect money from the local '7-11,' '' says Pike.
The extortion often aims at Vietnamese who run small retail outlets and succeeds without a need for physical threats. But law-enforcement officials say there are sometimes definite threats to harm the victim physically or to label him as a communist sympathizer.
Mr. Pike suggests that some, but not all of the funds are going back to Vietnam. ''Sometimes they say they are collecting money for the anticommunist resistance in Vietnam. Not all the money goes to Vietnam, but still the tradition of unrelieved greed is not strong in Vietnamese culture. There is often a Robin Hood element here,'' he says.
Last July, Lam Trong Duong, a community organizer thought to be sympathetic to Vietnam's communist government, was shot to death on a San Francisco street. In a letter to the Associated Press, a group calling itself the Anti-Communist Viets Organization claimed credit for the killing and accused the ''victim'' of being guilty of ''odius crimes against the Vietnamese people.''
A year ago, after a Harvard University panel discussion, an anticommunist former soldier named Nguyen Chau hurled a homemade bomb at one panelist, Vietnamese historian Ngo Vinh Long. The bomb did not explode, and no one was hurt.
Some anticommunist refugees have charged Mr. Ngo is an apologist for Vietnam's communist government. Although some academics praise Mr. Ngo's research abilities, others say he is sometimes abrasive and provocative when talking with anticommunist refugees.
The Ngo Vinh Long case led to an unusual legal decision that connected the assault with the war. In May a jury found Nguyen Chau not guilty of attempted murder by reason of insanity. Defense pychiatrists testified that his military experiences, including witnessing the execution of a close friend by communists, left him a victim of ''post traumatic stress disorder'' - sometimes known as ''Vietnam Syndrome.''
All this helps explain why authorities outside of the Vietnamese community find it a difficult challenge to cope with the violence. Law-enforcement authorities say it is extremely difficult to get a Vietnamese to testify in court for the prosecution.