The New York Times April 3, 1985, Wednesday, Late City Final Edition THAIS HOSTILE TO ETHNIC VIETNAMESE BYLINE: By BARBARA CROSSETTE, Special to the New York Times SECTION: Section A; Page 8, Column 4; Foreign Desk LENGTH: 1168 words DATELINE: UDON THANI, Thailand, March 27 Tens of thousands of ethnic Vietnamese living in Thailand are finding themselves in a precarious position as public anger mounts over daily reports of incursions into Thai territory by Vietnamese troops pursuing Cambodian guerrillas. In the last few weeks, large and well- orchestrated rallies to denounce Hanoi have been held in Thailand's Northeast, where most ethnic Vietnamese live. Most of these Vietnamese do not hold either Thai or Vietnamese citizenship, and they are vulnerable to pressures both from Thais and from pro- Hanoi Vietnamese within their ranks. While the organizers - Thai nationalist groups and Government officials - have said repeatedly that the anti-Hanoi demonstrations are not aimed at local residents, at least one rally, in the Mekong River town of Nakhon Phanom, was reported to have turned into an attack on local Vietnamese. No injuries or property damage resulted, Thai authorities said. But in Hanoi, the Thai Ambassador was summoned to receive a protest. Here in Udon Thani, the capital of a province with about 7,000 ethnic Vietnamese, residents say Thai hostility and Vietnamese fears have never been far below the surface. In 1979, the year Vietnam ousted the Khmer Rouge Government in Cambodia, rumors that Vietnamese were poisoning local food led to riots. Visitors are still told stories of secret Vietnamese contacts with Hanoi's agents across the Mekong in Laos. Thai officials who monitor the Vietnamese discount such fears, but they persist. Some in Thailand for Decades There are thought to be about 80,000 ethnic Vietnamese in the Northeast, where they entered the country from Laos or Cambodia. Some have lived in Thailand for generations and have become Thai citizens. But the overwhelming majority, denied Thai nationality, continue to exist, after more than 30 or 40 years, in a circumscribed condition of statelessness. They are barred from many jobs and most professional training and higher education. They cannot own property, though they are allowed to operate businesses. Their rights to travel, even inside Thailand, are severely restricted. Every Vietnamese over the age of 12 must carry a special identity card, the cover of which shows silhouettes of people in conical Vietnamese hats. This year, Udon Thani's provincial government banned the wearing of Vietnamese-style hats. A billboard has been erected here, complete with samples of Thai and Vietnamese headgear and the admonition to avoid ''alien hats.'' Another sign beside it exhorts the reader to ''be a real Thai'' by wearing the right hat. ''Be a free Thai, not the slave of other countries,'' it says. The other day, when anti-Hanoi protests were held in 17 provincial towns in the Northeast, including this one, a visitor asked a hotel clerk for the addresses of Vietnamese restaurants. The clerk replied: ''They will all be closed today because of the demonstrations. We don't like the Vietnamese, and they know that.'' Vietnamese Unwilling to Talk Vietnamese shops and restaurants were not closed, here or in Nong Khai province to the north, where the ethnic Vietnamese population is believed to be about 9,000. But proprietors did not want to talk about the day's events. In the river town of Si Chiang Mai, a center of Vietnamese settlement, a group of people making Vietnamese rice wafers in a family shop told a visitor, in Thai, that they were all Thais. Among the stateless Vietnamese in Thailand are people who fled into Thailand during World War II, when Indochinese nationalists were plotting against the French. Others, known as ''Dien Bien Phu Vietnamese,'' sought refuge during and after the final battles for independence from France. They came for many reasons. Some were politically or religiously motivated, as were the hundreds of thousands of North Vietnamese Roman Catholics who fled to South Vietnam. Many others were simply avoiding the disruption of war. A large number were driven away from Cambodia and Laos by anti-Vietnamese sentiment after the departure of the French, who had encouraged Vietnamese to settle there. Some Vietnamese were returned in the late 1960's, officials here say. Since 1975, when South Vietnam fell, Thailand has not allowed Vietnamese to settle. Instead they are confined to refugee camps to await emigration to other countries. Competition Between Empires The traditional antipathy to Vietnamese, going back over centuries of competition between Siamese and Vietnamese empires, is at least partly to blame, refugee officials say, for the brutality that Vietnamese boat people have faced from Thai pirates. Questions about Vietnamese security risks arise because many of them who have lived in Thailand for three or four decades cling to the memories and romantic hopes of early Vietnamese nationalists. ''In many of their houses the picture of Ho Chi Minh hangs higher than that of the Pope,'' a priest said. Thai officials responsible for the ethnic Vietnamese say that traditional loyalties like these have been exploited by pro-Hanoi factions. In an interview here, Capt. Charoen Phimsuksa, a Thai Army intelligence officer, said about 20 percent of the ethnic Vietnamese in this province may be donating money to Hanoi or gathering information to be passed on to the Vietnamese Embassy in Bangkok. But except for some direct support given a decade ago to a Communist insurrection in the Northeast, he said, ethnic Vietnamese have not been a danger to Thailand. A Potential for Trouble Thai authorities are aware of the potential for trouble that could come as new generations of ethnic Vietnamese, who were born here and consider themselves Thai, continue to be denied the rights of Thai people. Officials working most closely with the Vietnamese say that a disaffected group is being created and that Thailand should move toward granting citizenship. Political considerations and popular sentiment may make this a long process, however. ''In Udon, most Vietnamese people want to have Thai citizenship,'' said Lieut. Col. Sermsak Keokanta, the provincial deputy police chief in charge of Vietnamese affairs. ''The first step will be to make them resident aliens. Then, after they prove they are good people, they could get Thai citizenship on a case-by-case basis.'' At the same time, he said, ''officials in Udon try to explain to the Thais how to understand the Vietnamese better.'' Meanwhile, the ethnic Vietnamese try to stay out of the limelight and to demonstrate their loyalty to Thailand. A group of them, prosperous merchants, recently donated nearly $40,000 to the Thai Army to help defray costs of its operations against Vietnamese troops on the Thai-Cambodian border. It is hard to measure their anxiety, church workers say, because if they suffer, they do so in silence. A priest who has known many Vietnamese over the years said, ''Even I don't feel that I could go to anybody and say: Tell me how it really is.'' COUNTRY: THAILAND (97%); CAMBODIA (95%); VIETNAM (94%); LAOS (92%); CITY: HANOI, VIETNAM (94%); GEOGRAPHIC: ;THAILAND; VIETNAM; CAMBODIA THAILAND (97%); CAMBODIA (95%); VIETNAM (94%); LAOS (92%); HANOI, VIETNAM (94%); SUBJECT: FOREIGN POPULATION AND FOREIGN DESCENT GROUPS; REFUGEES AND EXPATRIATES; CITIZENSHIP; DEMONSTRATIONS AND RIOTS; SOCIAL CONDITIONS AND TRENDS; CIVIL WAR AND GUERRILLA WARFARE; ARMAMENT, DEFENSE AND MILITARY FORCES ARMED FORCES (90%); RIOTS (90%); CITIZENSHIP (90%); WAR & CONFLICT (90%); PROTESTS & DEMONSTRATIONS (89%); MILITARY WEAPONS (77%); REGIONAL & LOCAL GOVERNMENTS (75%); REFUGEES (74%); TRENDS (74%); RESTAURANTS (66% ); PERSON: CROSSETTE, BARBARA LANGUAGE: ENGLISH GRAPHIC: Map of Thailand highlighting Udon Thani; photo of signs in Udon Thani describing proper headgear (NYT/Jim Wilson)