Sakharov's relatives enjoy US, but worry about Soviet dissidents

When your stepfather is being held in internal exile in the Soviet Union, it's natural to be ''very concerned.''

But when he is Andrei Sakharov, the Nobel Prize-winning physicist and the USSR's leading dissident, the Western world watches with you.

Eight months ago Dr. Sakharov and his wife, Yelena G. Bonner, went on a 17 -day hunger strike to free Lisa Alekseyeva to join their son, Alexei Semyonov, in the United States. The dangerous strategy worked, and Lisa, who had married Alexei in a proxy ceremony, joined Alexei in Boston in a Christmas ''love story'' that proved an irresistible media event.

Now the young couple sits tanned and relaxed in the living room of the modest suburban home of Alexei's sister and her husband, themselves Soviet emigres. The media spotlight is off them, they say, but still on Dr. Sakharov and many others who suffer for challenging the Soviet state. ''There is continuing concern from scientific and human-rights organizations in the US as well as elsewhere in the world,'' says Alexei, a PhD candidate in mathematics at Brandeis University.

Dr. Sakharov, the ''father of the Soviet H-bomb,'' was exiled to the city of Gorky 21/2 years ago shortly after protesting the Soviet invasion of Afghanistan. He is not allowed to leave the city, 250 miles east of Moscow, which is off-limits to foreigners. He and his wife are ''closely watched,'' says Alexei, and occasionally harassed by the Soviet secret police.

The Sakharovs' hunger strike, say Western diplomats who follow the dissident scene in the USSR, set a trend for several others who have tried this tactic in an effort to join spouses in the West. Some have been allowed to leave; two others recently were told their visas would be denied for at least six months. Although the Semyonovs are pleased for the reunited couples, they feel more relief than triumph. ''It's very frightening, actually,'' says Alexei. But the strikes do ''show how many people are really desperate and ready to take steps like this.'' The dangers, he reminds, are real. ''It doesn't mean it's enough to just announce a hunger strike and then you will get permission to leave.''

Despite the imprisonment or exile of nearly all of the Soviet human-rights movement's prominent leaders, says Alexei, ''It would be wrong to say the movement (in the USSR) is a total failure. On the contrary, I think one should say it is a success, even though it's hard to say this when so many people suffer.

''Because of vhis movement the question of human rights was brought up and is going to stay up . . . even though the ways of achieving the solution of the problem are not defined yet. . . .''

The improvement of human rights in the Soviet Union will not be the result of an inevitable evolution toward personal freedom, says Alexei, who was able to leave the USSR four years ago. ''We should not hope that without pressure from the inside along with pressure from the West that the (Soviet) authorities themselves will allow some kind of freedom. What is needed is a very deep change in the society.''

The Semonyovs back President Reagan's stand against supplying equipment to build the Soviet pipeline to Western Europe, saying he is taking the larger world view. ''Europe is thinking in practical ways, but they are not ready to think in global terms,'' says Alexei. ''Whereas the United States, by the nature of being the imposed leader of the West, must be more concerned with that kind of question.

''Also, I would mention that the construction of the pipeline in Siberia is being done with prisoners, and in fact the credits given by the Western world to build this pipeline are being used to bring more prisoners to these places.''

For Lisa, there was little time to think about what life would be like in the US while she was struggling to leave her homeland. ''Now that I am here,'' she says quietly in Russian with her husband translating, ''I think it is very frightening to live in the Soviet Union. Since I have come, many more have been arrested. . . .''

She told of some friends who are still in peril.