"Long after Yuri Andropov will have been relegated to the dustbin of history, the free spirit of men and women in the Soviet Union will express itself in poetry, music and painting."

So said an emotional Rep. Tom Lantos (D-Calif.) as he opened a show of "Unofficial Soviet Art" at the Cannon House Office Building Rotunda yesterday.

Many of the artists in the show have been or are imprisoned. Others have been exiled to the West. Some, like Alexei Belkin and Vladimir Ovchinikov, have, within the past few months, had their work confiscated and have been threatened with arrest, according to e'migre' Russian dissidents at the exhibition.

It is hard to imagine what most of them might have done wrong. There are, to be sure, a pervasive melancholy and an occasional symbolic wail, along with specific digs at Russian life: a painting from the '50s makes disturbing reference to Stalin and his mental hospitals--a man stands before one of them, holding brains in his hand.

But mostly these are artists searching for ways to express themselves, and they do it in highly professional ways. If there's an esthetic problem with this show--which includes everything from realism to fantasy to pointillism to semiabstraction and abstraction--it is that it is so tame.

"Socialist realism is a matter of dogma in art and literature . . . and you believe it. Period," said Alexander Glezer, director of the Museum of Russian Contemporary Art in Exile in Jersey City, N.J., which lent the paintings to the show.

If you've never heard of his three-year-old museum, you are not alone.

"It has been a real struggle," said Glezer, an exiled poet who organized the famous outdoor art show bulldozed in Moscow by the KGB in 1974.

He then said: "When Andropov came to power, there was a lot of speculation among western journalists about liberalization. They said he's a liberal, he plays tennis . . . he even likes abstract art. Now he has shown us what kind of a liberal he is. As soon as Andropov came to power there began a broad offensive against dissent, and just within the last few months, several people have been condemned and have been given very long terms of imprisonment in the camps. I think he has decided to finish with the dissidents."

He listed specific cases, including:

Leonid Borodin, a Moscow writer, arrested in April and sentenced to 10 years in a labor camp and five years in internal exile.

Galina Ratushinskaya, a young Kiev poet, recently sentenced to seven years in labor camp followed by five years in internal exile.

Alexander Kalugin, a Moscow artist who in early May was put in a mental hospital.

He also said that in April and May there was a "wave of searches in homes of conceptual artists, with work confiscated and warnings issued."

The most highly publicized arrest was that of artist-cartoonist Vyacheslav Sysoyev, who was also well-known outside the USSR. Underground since 1979, Sysoyev was arrested Feb. 8 and sentenced in May to two years in a labor camp.

"It was only two years, instead of the usual seven or 10 years," said Glezer, because a big international defense committee was formed and the case was highly publicized both here and in France and Italy. "They do benefit from such a response. But the American press has lost interest."

In the case of Sysoyev, whose satirical cartoons make fun of bureaucratic blockheads and openly deal with the loss of human rights, it is not wholly surprising that he has roused some official ire.

As to the poetic paintings of the recently harassed Vladimir Ovchinikov, however, one can only look in wonder at any attempt to squelch them. "Angels in a Shyvalova Station," on view here, is a realist fantasy in which people waiting for a train treat the presence of three angels as an everyday event. There are tanks on a freight train in the background, and possibly some hidden, hostile meaning. But for western eyes this is likely to be the most moving and beautiful painting in the show. This artist deserves far greater exposure in the West.

In case anyone doubted that persecutions actually take place, Mihail Chemiakin, 39, now exiled in France, was at the opening to bear witness. An abstract painter at 27, he was imprisoned in a Moscow mental hospital, where he said he was tied to a table as colored lights flashed before his eyes.

"Through the earphones came words like 'Mother Russia' and names of artists like Picasso. The only thing that kept me going was that they kept making mistakes and mispronouncing names. When I saw 'Clockwork Orange' later on, it reminded me of those days."

This show--the first official act of the cosponsoring Congressional Human Rights Caucus--came about through the efforts of Lantos and his wife Annette. Both were Holocaust survivors in Hungary during World War II and lived briefly under the subsequent Soviet regime.

Annette Lantos spent three years on this project, she said, because "these artists go to the Gulag for this, then nobody looks."

The exhibition, which continues through July, is open to the public in the Cannon Building Rotunda from 7 to 7 Mondays through Fridays, and Saturdays from 7 a.m. to 1 p.m. A smaller display of some good works on paper and several paintings is also on view in the Russell Senate Office Building Rotunda through Friday.