Back home in Vietnam, he was Le Van Tan, a commmando working with the U.S. Special Forces. Times have changed, though, and he now is Seif Hassan Ali, a bank clerk trying to integrate his almond-eye-family into the alien world of North Yemen.

"We are not happy in this country," complains his wife, Weng Ke Man.

The couple and their three children are among more than 500 Vietnamese who have turned up in North Yemen since the fall of Saigon in 1975. Many are of Yemeni ancestry or, like Weng, the wives of Vietnamese who trace their origins to Yemen.

Their arrival here, however, has turned out to be less than a homecoming. It has produced an unusual clash of Asian and Arab cultures, in large measure isolating the refugees from the closed Islamic society of North Yemen despite the Yemeni blood in their veins and the vague traces of Arab features in their Asian faces.

Most of the refugees are Moslems, descendants of Yemeni or Malay merchants who left children in their wake generations ago. But the tolerant Islam of Southeast Asia, they have found, is different from the conservative Arab variety practiced in the narrow streets of Sanaa or the craggy hills surrounding Taiz. In addition, the Koranic verses they memorized as children in a Saigon mosque have been of little help in learning the choppy Arabic spoken by Yemenis.

As a result, a few of the Vietnamese have put down genuine roots in North Yeman. A handful of enterprising families run restaurants serving Oriental and Yemeni food in Sanaa, the capital, or Hodeida, the main seaport on the Red Sea. But many are unemployed and more than half remain apart in a sordid little compound of one- and two-room apartments on the edge of Taiz.

Only one Vietnamese bachelor has found a Yemeni wife and a half-dozen Vietnamese girls have married Yemeni men in the four years since their families fled Vietnam. Some girls have gone into hiding to escape marriages arranged by their families with Yemeni villagers.

"They are afraid to go into the villages in the countryside," explained Weng Ke Man. "The Vietnamese girs can't work like the Yemeni women. In the city, it's better. But you know the Moslem law. The man is up on top, the woman is down on the bottom."

Weng, 38, and Le, 39, live in two rooms with their three children and her aged mother. They pay $45 a month in rent for their part of the compound originally built to house Yemeni workers but turned over to the Vietnamese in 1976.

The family fled Vietnam in a Red Cross plane that brought them to North Yemen under special arrangements ordered by the Yemeni president at the time, Ibrahim Hamdi. Le could trace his origins to Yemen but neither he nor Weng had any yearning to come here. Both had worked with the American military, in Vietnam, however, and they feared for their safety if they remained. This was the only possible destination.

"They would have killed us if we didn't leave," said Weng in the fluent English she learned as a secretary for a U.S. village pacification study team in Saigon.

She and Le also speak French and have found jobs in a local branch of a French bank despite their lack of Arabic. With the money they earn, they are able to send their childen to a private school in Taiz where they learn Arabic and English. Each child's tuition is more than $1,200 a year but a rich Yemeni merchant, who gives scholarships to help Vietnamese, pays all but $100 per child.

For those who cannot afford that, the Yemeni government has opened its free schools to the Vietnamese.

"There used to be about 40 in the Arabic school," said Weng. "Then they left, one by one, because they don't understand. The teacher tells them things, but they just don't understand what he is saying."

Yemenis also find much of what the Vietnamese say and do strange. The Vietnamese women walk in the streets without veils and wear pajama-like trousers instead of the black multi-layered robes that hide the shape of Yemeni women.

This has contributed to a local misapprehension that the Vietnamese women are available for the asking. Two Yemeni men eying a Vietnamese woman lounging in her doorway at the compound recently were overheard to say:

"She has just been sitting there inviting me for the last hour."

"You mean you could have gone inside with her?"

"Yes, of course. That's the way they are."

As Weng and Le received a pair of visitors, she sat and talked freely, interrupted Le frequently and, on one occasion, let down her hair and rearranged it in a pile on top of her head. This was a sharp departure from tradition in a country where women rarely join their husbands with male guests. t

Language problems often complicate such conflict in national customs. Vietnamese invited to a Christmas party by a Taiz doctor were arrested on their way back to the compound and jailed for several days in confusion over what they were doing in the streets late at night.

Despite their troubles, however, many Vietnamese appear glad to be out of Indochina. Interviews in the compound showed that most had some connection to the fallen South Vietnamese government or to the French or U.S. military and feared reprisals after the Communists assumed command.

Hassan Mohammed, who was Wan Dum Sung in his Vietnamese days, said he became frightened when the Vietnamese Communist authorities began a review of citizen's identity papers to trace their past because he had been an agent of the French intelligence service. "With my papers, man, I was really scared," he said.

So when the Yemeni consul in Saigon came knocking at his door, Wan gratefully accepted the offer of emigration to North Yemen. He brought his wife and seven of their eight children. One daughter remained behind, along with what he said were about 40 Moslem families in the Saigon area.

"They also want to leave now," he said. "Anywhere, any country."