Throughout the Soviet Union, there may be no place exactly like this one: a two-room Moscow apartment where conversations -- intensely intellectual, frequently funny, always lively -- in Russian, English, or German proceed from midmorning to late at night.

The visitors are young Soviet poets, Soviet jazz musicians, literary critics, older poets and writers, chemists, social researchers, physicists and retirees. Some are elderly survivors of Stalin's prisons. Some have been expelled from official writers' unions or scientific institutes. Some are simply friends risking their official jobs by dropping by.

Jumbled into this mix are Western correspondents, visiting European and American tourists, intellectuals, authors and publishers, and sometimes, Soviets with social grievances looking for a sympathetic ear. The apartment is a place of surprise, distraction, and continuous activity as people troop in and out.

This is the home of Lev Kopelev, a prominent Soviet literary analyst and historiographer, a writer with a growing audience in the West and a friend of both Andrei Sakharov and Alexander Solzhenitsyn.

Although he has neither the fame of a Solzhenitsyn nor the worldwide moral stature of a Sakharov, Kopelev and his wife Raisa rank close behind them in importance in the context of present-day Soviet life. The discussions at their home provides a kind of switchboard for intellectuals of every sort to plug in, cross-connect, and transfer ideas. In a country where such unofficial free exchanges are frowned on and can bring reprisals, the Kopelevs occupy a place of unusual significance.

Now they, too, are under attack from the authorities for their persistent defense of Sakharov, who was exiled to the industrial city of Gorki last month, and their friends and acquaintances are deeply worried for their future.

Kopelev, 67, was bitterly denounced Feb. 3 by an official newspaper as a "Judas betraying his people and country . . . who smuggles abroad lampoons" that defile the Soviet state. His apartment was called "a nest of ideological subversion."

The attack was apparent retaliation for Kopelev's participation in the defense of Sakharov by Soviet dissidents, who have called for his release from exile. For Kopelev, the plight of the 1975 Nobel Prize laureate has painful personal dimensions.

The two met at a poetry reading here in the early 1970s. At the time, Sakharov had turned away from the Soviet hydrogen bomb program to take up human rights causes. Kopelev, a once-zealous communist despite being imprisoned nearly 10 years during the rule of Joseph Stalin, had then been expelled from the party for the second time for publicly protesting the persecution of Soviet intellectuals.

"We talked poetry and ideas about verse," Kopelev said yesterday, recalling the moment. But Sakharov eventually became yet one more in the eclectic collection of friends of the white-bearded, barrel-chested Kopelev.

The two men with their wives vacationed together in Zhukovka, the secluded retreat outside Moscow where Sakharov had been given a dacha by the Kremlin, and for the past two years, the couples rested in Sukhumi on the Black Sea. Last fall, Sakharov delivered two lectures there to the Kopelevs on the origins of the universe, the physicist's current scientific work. Kopelev later helped translate them into English, as required by the Lebedev Institute of the Soviet Academy of Sciences, where Sakharov studied despite his official ostracism before exile.

"Those were very good and fulfilling times," Kopelev said. "Andrei united absolute morality and tolerance . . . His is a very Russian character, righteous and modest. My field is literature so I can make these comparisons . . ."

Kopelev occupies a unique position in the eddying currents of East-West relations. His analyses of novelist Heinrich Boll's work drew a literary coterie to him in West Germany 20 years ago that has grown to major proportions. Boll and Kopelev met in 1962 and formed a close friendship. They have appeared on joint television interviews numerous times discussing modern life and literature in a way that has brought Kopelev a wide following.

Kopelev's best-known work in the West is "To Be Preserved Forever," one of an autobiographical trilogy in which he explores how he embraced and then rejected communism. The book has been published in 10 languages, and two other volumes, "He Worshipped Idols," and "Assuage My Sorrows," are being prepared for publication in English. Solzhenitsyn's "The First Circle" also presents a fictional rendition of Kopelev as Lev Rubin, a communist who has not lost his faith despite being a victim of Stalinist retaliation.

Sakharov's exile Jan. 22 struck hard in West Germany, and the subsequent denunciation of Kopelev has triggered new outcries from Mowcow's most important capitalist trading partner. In recent years, Boll, a 1972 Nobel literature laureate, and other prominent West Germans have invited Kopelev there for lectures and scholarly research. Soviet authorities have either refused temporary exit permission or refused to say whether they would allow Kopelev back into the Soviet Union once he left. Without such a guarantee, he has refused to leave.

But one of children, Maya, who lives in Tarrytown, N.Y., with her husband, Pavel Litvinov, a grandson of 1930s commisar of foreign affairs Mazim Litvinov, has asked the authorities to allow her father and step-mother to leave. Kopelev, who was expelled from the Writers' Union in March 1977 after a new defense of Sakharov, is torn in new ways by the calls from abroad and the new crackdown of free expression inside the country.

"Before, I decided I would stay so long as I could be of help to people," he said. "Now, nothing is clear."