Two-Way Exchange of Smiles. Increase in student exchanges reflects new warmth in Soviet-American relations. COLD WAR THAW

THE future of Soviet-American relations is written on the face of Marina Yamburenko. A year ago, the pretty 16-year-old could not have imagined herself visiting the United States - certainly not as a high school student, and probably not in the course of her lifetime as a citizen of a nation with a 70-year history of closed borders.

Now, fresh from a ground-breaking five-week exchange visit to Tucson, Ariz., she bubbles with enthusiasm.

``It was wonderful!'' she says in easygoing English, recalling her stay in the home of an American family she called ``Mom'' and ``Dad,'' and her classes at Green Fields Country Day School, a private school.

Wonderful, but not necessarily relaxing. Under the terms of the exchange, the students visited 22 other private and public schools while in Tucson, coming in contact with more than 5,000 American students. In addition, they touched millions more through dozens of television, radio, and newspaper stories and interviews.

Now that Marina has caught up on her sleep, what's her abiding impression of all that effort?

``Everywhere we came to visit schools and people, they met us with such hospitality,'' she says. ``Always smiles.''

Her delegation - seven students and two teachers from Public School 155, a drab concrete building tucked behind apartment blocks near the center of the Soviet Union's third-largest city - charted new territory. Reflecting the continuing ferment of perestroika and the progressive decentralization of Soviet authority, it was the first US-USSR exchange of junior high and high school students to be negotiated at republic level - approved only by the Presidium of the Ukrainian Soviet, without oversight from Moscow.

As such, it stands as a cameo of the ways in which the thawing of cold-war tensions has warmed relations at the most basic levels in both nations.

The thaw that brought Marina to Tucson dates from 1985. That November, in Geneva, President Ronald Reagan and Soviet leader Mikhail Gorbachev signed the General Exchanges Agreement, reinstating agreements terminated by President Jimmy Carter after the USSR invaded Afghanistan in 1979. Since that Geneva meeting, exchanges have spiraled upward - in sports, music, the arts, professional groups, and academic programs.

Many have operated through government-to-government contact. But not the Kiev-Tucson link. It began when George Kostilyov, principal of the English-emphasis Public School 155, appeared on a home video made by a group of visiting artists from Tucson and said he was eager to develop an exchange with a US school.

Back in Tucson, Phineas Anderson, the headmaster at Green Fields, saw the video and wrote to Mr. Kostilyov. ``We both got really enthusiastic, pumping each other up,'' says Mr. Anderson, contacted by phone at his office in Tucson. ``We think alike, we know how to move our mutual bureaucracies, we're both organized, we both have the same desire for this generation to move forward and appreciate each other.''

Spurring each other on in weekly telephone calls, the two principals laid the groundwork for the exchange. By last June, Anderson had assembled the funding he needed - $20,400 from the Samantha Smith Memorial Exchange Program of the United States Information Agency (USIA), and the balance from a Tucson family.

Then, in October, he visited Kiev, where Kostilyov arranged high-level visits with representatives from the Ukrainian Peace Committee (the major Soviet funder), the People's Committee on Education, and the Youth Organizing Committee. ``Once they signed off on it,'' Anderson recalls, ``they moved extremely quickly.''

Now, after 14 months of effort, the Kiev students are home again - and currently hosting seven students and two teachers from Green Fields at what Kostilyov proudly describes as ``one of the first citizen-diplomat schools'' in the Soviet Union.

In fact, the honor of being the first was swept away by the rapid momentum toward high school exchanges. Under the terms of the US-USSR High School Academic Partnership Program, a protocol signed last Oct. 1, 30 US high schools received almost 400 Soviet exchange students for month-long stays in private homes in January. A corresponding number of American pupils then went to the Soviet Union.

When the USIA-sponsored program is fully operational in 1990-91, it will maintain lasting exchanges between 100 US and Soviet schools involving some 3,000 students each year.

And that is ``revolutionary,'' says Robert Persico, deputy director of the USIA's Youth Exchange Staff. Until two years ago, he says, there were almost no two-way high school exchanges between the US and the Soviet Union. ``On the whole, the Soviets were reluctant to allow their children to come here,'' he says, adding that they were especially leery of allowing students to live in private residences.

Under perestroika, however, the number of exchanges has exploded. And the fact that the students are staying in private homes is, he says, ``extraordinary.''

All of which has benefited Marina and her friends here at Public School 155. Even the fact that she is wearing a colorful, hand-embroidered vishivanka, part of the national dress of the Ukraine, speaks powerfully about recent changes.

Only in the last few years have Ukrainian customs and language, rather than the Russian culture imposed from Moscow, been allowed to flourish openly here. Now Kostilyov has no qualms about entertaining a group of visitors to Public School 155 to a half-hour student program of Ukrainian songs, skits, and folk dancing.

What have all the changes meant to Marina? Coming back to Kiev, she says, was ``a little hard, because I left all my friends again.''

But the exchange has made a deep impression on her. ``When I came back, I felt some differences and changes in myself. I am more attentive, and I'm more positive now. It is a good experience for me, being in the United States and seeing all this.''

A top-level student whose family (like all those in the delegation to Tucson) are members of the Communist Party, she hopes to enter the Institute of International Relations in Moscow - although, she says, it will be ``very, very difficult to get in.''

For both Anderson and Kostilyov, having students like Marina eventually move to high-level diplomatic positions is the payoff for such exchanges.

``As you look at the world and the global economy,'' says Anderson from his Arizona office, ``you need to prepare students for this next century of ours to have an appreciation and an understanding of people different from themselves.''

From his battered wooden desk decorated with a pair of Soviet and American flags, Kostilyov agrees. ``Our need is to spread it,'' he says of his school's exchange program, now preparing to enter its second year. The goal, he adds, is ``to make it more solid, to make it profound.''