East or West, Teens are Teens. DIPLOMACY: SOVIET-US STUDENT EXCHANGE

THEY'RE back in Moscow now, filled with dazzling impressions: meeting Gov. Michael Dukakis; going to a Celtics game and talking to Larry Bird; sightseeing in Washington and New York; living in roomy individual houses as opposed to Soviet-style apartments; and shopping at malls and supermarkets unlike anything they'd seen at home. But most of all, said a group of Soviet high school students who spent four weeks here, they were struck by how alike teen-agers of the two countries are.

``We have the same interests - we like to go to parties, and we like music, sports, and TV,'' said 15-year-old Tanya Manzyuk.

Tanya was one of 10 students from Moscow School No. 27 who spent part of the winter at Buckingham Browne & Nichols School here and lived at the homes of American students as part of a historic exchange program. Tanya's impressions were echoed by her schoolmates, though Yuri Pivovarov, also 15, did point out one interesting difference.

``The US kids like to joke a lot more than we do, and they always look happy,'' he said. ``They must have problems sometimes, but they don't show it. We smile when we're happy, too, but if a Russian has a problem, he looks like he has a problem.''

To the BB&N students, one of the most impressive things about the visitors was their command of English. Their guests attend a school specializing in English, and have been taking it since second grade. Many of them speak fluently, with virtually no accent, and all are far ahead of where their counterparts are in Russian.

``They laugh when we do our drill sheets,'' said one BB&N ninth-grader. ``But the girl who was helping me said they were all really impressed at how much we have learned in so short a time.''

Despite the vast differences in culture, most of the visitors said they weren't surprised by what they found on their first trip to the United States. They said books, magazines, movies, TV, and talks with US visitors or Russians who had been there had given them a pretty clear picture.

``I like to read and watch movies,'' said Alexei Zaitsev, a 16-year-old from another Moscow school whose exchange is with Newton North High School, ``and thanks to glasnost we have lots of new movies showing American life which we didn't have before....''

``They really know a lot about he country,'' added Valentina Moryakova, the teacher accompanying the group at BB&N. ``In school we talk a lot about America. We have exams about the geography, the climate, the rivers, mountains, and cities, the political system. And whenever we can, we bring in exchange students or other visiting delegations.''

Each country's school system has things that make students from the other one a bit envious.

``It would be nice to go to school only five days a week and to be able to choose some of your subjects,'' said Tanya, noting that the Soviet school week is six days, and all subjects are compulsory. ``On the other hand, they spend more time on homework.''

This first-ever full-scale exchange of high school students between the two countries grew out of agreements signed by President Reagan and General Secretary Mikhail Gorbachev during the Moscow summit last May. Students representing 30 schools throughout the Soviet Union launched the program by visiting a like number of schools all around the US this winter, with return visits by the Americans to the USSR coming up in March and April. About 350 students from each nation are participating this year, with the numbers scheduled to increase in ensuing years.

Just about everyone on both sides was struck by how quickly and deeply an emotional bonding took place between the students and their temporary families.

``It was amazing how quickly it happened,'' said one parent. ``After just a day or two, we'd pick her out as `our kid.' We feel as though we have three daughters now instead of two. Now that she is gone, we have a sad feeling that we never expected beforehand.''

Ms. Moryakova also noted this phenomenon. ``They all talk about their `brothers' and `sisters,''' she said on the eve of the flight back to Moscow. ``And with the parents you hear them saying, `There's my mother,' or `That's where my father works.' [The students] miss their families and friends at home, of course, but some of them have been so happy here that they wish they could stay longer.''