Although Soviet high schools are very different from their American counterparts -- police patrol the dances to watch for too much fraternization, for example -- some aspects of teen-age life are universal, as a group of American students recently discovered during an exchange visit.

Smoking in the bathrooms. Skipping class. Even some cheating on examinations.

"The students wrote answers on their arms, and sewed them into the lining of their clothing," reported Rebecca Toth, 18, a senior at Reston's South Lakes High School and one of 48 American high school students who attended Soviet schools for three weeks in April.

The visit is believed to be the first by American students in Soviet high schools, say the sponsors from the School Exchange Service in Reston. Toth was one of six South Lakes students who made the trip. Organizers hope for a reciprocal visit by Soviet teen-agers next year.

A before-and-after survey of the teen-agers showed the visit to be an eye-opener. Before the trip, most of the American students did not disagree that Soviet teen-agers were "different than I am." Afterward, 55 percent disagreed.

After the trip, teen-agers were also more likely to believe that Soviet students are politically outspoken and that religion is important in the Soviet Union. Perhaps most important of all, they discovered that the Irish rock group U2, which is popular with American teen-agers, also is popular there.

On foreign affairs issues, more students said "nuclear weapons are necessary to protect the U.S." after the trip, but more of them also said additional government money should be spent on social needs rather than the military.

Toth, who will deliver the South Lakes graduation speech tonight, and Dustin Pons, 18, who graduated this spring from John Carroll High School north of Baltimore, spoke at a news conference yesterday at the National Press Club in downtown Washington.

Toth attended Soviet School 69 in Moscow, an elite academy for students specializing in English, where she took classes such as Russian language and literature six days a week, a stricter academic schedule than at most American high schools.

Toth had expected "tough, leatherneck teachers," but was surprised to find a casual classroom atmosphere. Class content emphasized memorization more than critical thinking, the American students said.

The Soviet students were well informed about American rock groups, but they had some curious misconceptions about American life, the returning students said. "When I told my Soviet friend that American night life starts at 9 o'clock," Toth said, "he said, 'I understand American night life. It's called prostitution.' "

Pons, who attended school in Leningrad, said he had expected the Soviet students to be "rigid and strict," but found them "open and friendly, like us . . . . They just want to have fun." However, after school, he added, they were more likely to read a book or take a walk than their party-going American counterparts.

The Soviet students have only limited knowledge of global current events, and most believe that the United States is an aggressive country, the two Americans said. The Soviet students criticized as unrealistic the ABC miniseries "Amerika," which depicted a fictional Soviet takeover of the United States.

The Soviet students voiced some criticism of their government, but "they loved their homeland and they'd rather be there than any place in the world," Pons said.

The same for the Americans. "We all returned with a much stronger national pride," Toth said.