Hang Phuoc is a quiet, attentive 17-year-old Vietnamese boy who should fit right in with his fellow students at Montgomery Blair High School.

He takes algebra, U.S. history, science and English instruction.

But Hang has special problems because he spent last year in a Malaysian regugee camp, without formal schooling and only a month of English.

He is eager to learn, but the gap in his education will not narrow while he struggles to learn English.

His is a situation shared by hundreds of foreign students throughout the county, and one the U.S. Department of Education is trying to solve by requiring transitional bilingual teaching -- instruction in the native language along with the introduction of English words.

The department in August issued guidelines to make sure schools afford equal educational opportunity to students who speak little or no English, primarily by requiring them to hire bilingual teachers' when there are 25 or more students of the same language backgrounds in two consecutive grades.

The Montgomery County Board of Education voted to oppose the guidelines and sent a board member to represent its position at public hearings in New York City earlier this month.

The board said in its statement that transitional bilingual education alone is not the panacea for the problems of the county's diverse foreign student body. About 2,400 of those students speak little or no English. They are distributed throughout 161 schools and speak 83 different languages.

For about 200 students from the country's largest foreign groups -- Hispanic, Korean and Vietnamese -- bilingual classes began last year at six schools. Another 330 students in about 12 schools take English language modified math, science and history courses.

But as the foreign student population grows rapidly, with Vietnamese, Cambodians, Cubans, Nicaraguans, Afghanis, San Salvadorans and others whose families left politically turbulent homelands, the school system struggles with a foreign student body that has a 45 percent turnover yearly and defies orderly assimilation. The high turnover occurs as refugee families move about until they settle permanently, and as the children of diplomatic families and those employed by international firms and organizations come and go.

The foreign students come from every conceivable educational background. Some have no academic record, or even a passport.

"When you have a different language, culture and school system to start with, and add to that having been out of school for x number of years, there are real problems," said Frank Fernandez, head of the International Students Admission Office.

"Montgomery County seems to be getting more students who've had less training. We've noticed that in this office. We've been getting kids who had been in (refugee) camp for two to three years and had no formal training during that time," he said.

"The way it is now they're replaced according to age, and we also get a lot of wrong information from parents," said Ton That Toai, a Vietnamese psychiatrist working half-time for the Montgomery County school system and half-time for Arlington schools.

"The students need to be tested in their native language," he said.

Because such tests are not available, many students are put in classes that are too advanced for them, or they spend most of their time in the program called ESOL, the acronym for "English for Speakers of Other Languages."

ESOL is, simply, an English course for foreigners. It is taught for an hour or two daily -- or in some cases, most of the day -- depending on how much English the student speaks. It has been used for the past dozen years, and currently about 2,300 students are in the program.

The ESOL/Bilingual Division of the school system devised this summer a series of interviews and evaluation sheets for ESOL teachers to use in deciding when a student knows enough English to regular classes.

"It's hard, sure, but these are the problems that immigrants have always faced," said Jessie Diffley, who teaches a modified social studies course at Montgomery Blair High School. "They learn quickly and education is important to them."

In her social studies class, which is a survey of U.S. history, Diffley starts out with the geography of the United States and tries to give the students a lot of information that will prepare them for the responsibility of citizenship.

"The challenge now is to individualize the programs," said Betty Knight, director of the ESOL/Bilingual Division. "We need to take care of those with learning problems and those who aregifted, who are in some way not at the norm. I suspect the resources are going to be limited, so we have to get the data now and the programs going," she said.

For a start, Maria Carbonell, a psychologist whose native language is Spanish, is working fulltime this year to develop a multilingual network of psychologists.

"Among students who are subjected to a change of culture there is a larger potential for emotional handicaps," she said.

But the concern, she emphasized, is not to label a child handicapped while he is still learning English.

The ESOL/bilingual operating budget for the year that began July 1 was $1.7 million, up from $1.2 million from the year before and $902,720 in fiscal 1979. About, $200,000 is from federal funds.

Knight said while the addition of bilingual education and 24 ESOL teachers, to make a total of 76 last year, was badly needed just to catch up, "We expect to have one of the most comprehensive programs for the LEP (limited English-proficient) student in the country.

"We are not going whole-hog in one direction. There is strong accountability," she said.

She said she feels the program answers the needs of foreign students for the time being, barring a sudden influx of a particular language group of students.

"Eventually, we'd like to see kids in the country clustered," she said, as is being done at Northwood High School and Col. Joseph Belt Junior High School, to which 183 students are being bused. They take bilingual, modified and regular courses, as well as English instruction.

"Here (at the two schools) we can use staff to optimum and centralize resources. This way we get a much better program," she said.