WHEN THU TRUONG was in Vietnam, she always felt different.

"When people would look at us and see our high noses, they knew we were Amerasians and treated us differently."Even in class, the teacher would look at you and treat you another way."

Thu, 21, and her sister, Trang Truong, who will be 17 next month, are among thousands of children fathered by American servicemen during the Vietnam War. Offspring of the former enemy, they were outcasts in their homeland.

Nearly two years ago, the girls and their mother fulfilled a long-time dream when they arrived in the United States. About 50 Amerasian young people now live in Utah, and that number is likely to grow under an agreement reached in January that will expedite Amerasians' departure from Vietnam.

Jeff Davis, director of the Catholic Community Services foster care program, said the agreement is a continuation of the existing Orderly Departure Program, not a massive new airlift. It ironed out differences between the United States and Vietnam, which didn't want to release the children as refugees because it considered them U.S. citizens.

Nancy Schulz, coordinator of children's service for U.S. Catholic Conference Migration and Refugee Services in New York, said nobody, including the Vietnamese government, knows how many Amerasians there are. "Estimates go up to 30,000, but it's my personal feeling that that's a very high estimate." Because the war ended in 1975, the

children are now teenagers or older.

About 4,000 Amerasians have already been settled in the United States. Schulz said the Vietnamese government would like all Amer-asians resettled, and under the legislation the United States will take all who wish to come.

Khi Thi Truong, Thu and Trang's mother, joined the South Vietnamese Army and was working for an American adviser when she met the girls' father. They began living together in 1966 and in 1967 Thu was born.

In 1969 he was called back to the United States. He returned a year later and she bore Trang.

In 1973 he left Vietnam for good.

"When the communists came we were very scared," said Khi.

She was luckier than some. Her brother, an engineer, and sister, a pharmacist, helped support the girls. They had also worked for the Americans, but because their skills were so badly needed they kept their jobs under the communists.

That was a lifeline for Khi, because as a mother of Amerasian children she couldn't get a job. Nor could she get permits to buy food or clothing. "If I were still in Vietnam I must buy on the black market."

Her children were able to attend school, unlike most Amerasians. But Thu's university application was denied. "They looked at my resume and saw I was a Catholic and an Amerasian."

Many weren't so lucky, said Khi. "The mother has no job, they don't have clothes to wear or food to eat. Most live in the park."

Homeless Amerasian children sleep in doorways and sell cigarettes to tourists in front of hotels to survive, Thu said.

Khi said her daughters' future was bleak. Because their father was American, they wouldn't get jobs or higher education.

In 1982 she started trying to get permission to leave. "It takes at least three years. They try to make money from us, so they don't let us go early," Thu said.

Khi doesn't know where the girls' father is. "He's married and I don't want to bother him."

Coming to the United States, she said, was her dream. "Now it's come true, and I'm very happy now."

She works in food preparation. Thu, who married a young Vietnamese refugee she met in Utah shortly after they arrived, attends Salt Lake Community College, majoring in data processing. Trang goes to South High School.

They said people are sometimes surprised when they start speaking Vietnamese. Khi said both girls have put on weight - Thu weighed about 80 pounds when they came to the United States. "Here they drink milk. We didn't have milk because you must have a permit to buy it, and the black market is very expensive. My children are getting big, healthy. I like that."

While the material abundance of America amazed them, more important is freedom, Khi said.

"Here I have freedom. I like to work, and I have a job to work.

"I am very happy. I love America."

Moon Ji, state refugee affairs director in Utah, said he is not expecting an influx of Amerasians. Some will probably come to Utah if they have relatives or friends here.

Davis said most won't come alone. "We believe the vast majority of these kids have been with family. It may be the birth mother, grandparents, other relatives or a family friend. These people really love them and care for them, and when they come to this country, if they do, those people would come with them."

Ji said Amerasians may look like Americans, but their language and culture is Vietnamese. "They have a kind of identity crisis."

Joan Gardner of Catholic Community Services said it's difficult to generalize. "Some do really well, amazingly well. Others have definitely had a hard life over there and haven't had much schooling at all.

"Between the language barrier and then being placed at age level (in school), it's just too much for some."

Ji said that, by and large, Utah's Amerasian youngsters are doing well. He said that because of discrimination, their survival skills may be more highly developed.

Davis said some who come without family have fantasies about finding their fathers. That's a sensitive issue for resettlement agencies. "What is our responsibility as agencies to assist kids in locating their fathers, and what are the fathers' rights? How do we protect fathers who have closed this chapter of their lives and don't want to be reminded of it?"