MOSCOW -- Roy Medvedev made sense of his life as a dissident and historian during an investigation by the KGB. "Comrade Medvedev, tell me, please," an officer said. "Would you have written your books about Stalin if your father hadn't been sent away to the prison camps?" It was the mid-'70s, a period when the KGB regularly invited Medvedev to the Lubyanka and Lefortovo prisons for such discussions. By then, Medvedev had already won a reputation in the West as the most independent historian in the Soviet Union, a brave scholar who openly conducted interviews with old Bolsheviks and assembled unprecedented accounts of the Stalin era, including the definitive Soviet study "Let History Judge." Roy's identical twin, Zhores, won similar attention from Western scholars -- and from the KGB. Zhores was Roy's equivalent in the scientific world, a biologist and gerontologist who dared to write about the abuse of genetics under Stalin and the use of psychiatric hospitals to detain political dissidents under Brezhnev. In 1970 the authorities declared that Zhores suffered from "paranoid delusions of reforming society" and threw him into a psychiatric hospital for three weeks. It took a worldwide campaign, organized by Roy, to win his release. The KGB was forever harassing the Medvedevs. They confiscated their papers, pestered their families, intercepted their mail. In Moscow, Roy's wife got anonymous phone calls telling her that her husband was carrying on illicit love affairs and thought she looked like a "baboon." Zhores was finally exiled to England in 1973. Neither man could publish his books where they were most needed -- in the Soviet Union. The brothers had chosen the most difficult paths, and so now Roy Medvedev began to turn the KGB investigator's question over in his mind, again and again: "Why?" No one had ever posed the question to him so directly, or with such perverse intent. "I realized then just how closely my destiny was intertwined with my father's," he said here the other day. "It all came back." Moscow, Aug. 23, 1938. A knock on the door in the middle of the night. The sound of unwelcome guests. Startled from a deep sleep, two 12-year-old boys, identical twins, fair and thin, sat up in bed, trying to make out the muffled commotion outside the bedroom door. "Why do you come so late, comrades?" they heard their father say. No answer. Or at least nothing coherent. For weeks the boys noticed that their father had been depressed, eating almost nothing, sleeping less. It was a mystery to them why their father Alexander Medvedev, a respected officer in the Red Army and a popular philosophy professor, had been fired from his job. It was a mystery to them why the director of their Pioneer camp abruptly sent them home in the middle of the summer session. There was terror in the air, rumors of arrests and prison camps. Some of the family's friends had already disappeared in the night. But the boys, lacking an imagination of so colossal an evil, did not understand what their father understood only too well. In their youth, they could not make sense of this moment in the dark that would shape the rest of their lives. So Roy and Zhores dropped off to sleep. When they awoke early the next morning, the visitors were still there, opening and slamming cabinets, moving furniture carelessly, angrily. The bedroom door opened, and the boys' father walked in. He was dressed in a military tunic, but wore no belt and he seemed disheveled, as if he'd been up for days. He sat down on the bed and embraced his sons. There was something final and desperate about his grip. Zhores still remembers the feel of his father's prickly, unshaven face scratching against his cheek, how his father's wordless terror was so obvious that all three began to cry at once. And through the open door, Zhores could see agents of the NKVD, Joseph Stalin's secret police, searching the apartment and getting ready to take Alexander Medvedev off to die in the gulag archipelago. Roy and Zhores Medvedev are 63 now. Their faces have grown soft and wise in the same way. Their blue eyes gleam. Zhores is infinitesimally thinner, a determined walker on the streets of outer London. He wears a beard that speaks more of neglect than vanity. Roy is clean-shaven, trig, courtly, correct, foxy. When Zhores left for London, Roy assumed his role as the public Medvedev, an important and open source for foreign journalists and scholars who come asking about Soviet history and Soviet gossip. The brothers have not seen each other for 16 years. "We talk all the time and we still assume the lines are tapped," said Zhores, who once published a masterly little book on the history of postal surveillance and the KGB. In the '70s, the Medvedevs were principal players in the dissident drama, one corner in a triangular debate that included physicist Andrei Sakharov, who emphasized human rights and Western pressure on the Kremlin, and novelist Alexander Solzhenitsyn, who yearned for a Russia that would abandon the alien phenomenon of Marxism and return to ecclesiastical, prerevolutionary roots. As socialists and democrats, the Medvedevs hoped that a liberal, anti-Stalinist faction within the Communist Party would one day seize its moment, take power and try to institute a program of radical democratization and economic reform. Read today, Roy's 1975 book "On Socialist Democracy" sounds like a more thorough and scholarly version of Mikhail Gorbachev's 1987 manifesto, "Perestroika." "Both of us had always seen at least a seed of reform in a very dark earth," Zhores said. In an extraordinary sequence of events during the Gorbachev era, Roy Medvedev rose from vilification (and a full-time KGB guard outside his door in the early '80s) to a seat in the Congress of People's Deputies, the new legislature that opened yesterday. He has given a press conference at the foreign ministry, appears on television talk shows, gives lectures and now employs a team of research assistants who try to keep up with his scholarly and legislative business -- and he is expected to be elected to the Supreme Soviet. Yesterday, he spoke to fellow members of the new Soviet parliament. "It's strange, but somehow I'm unfazed by it all," Roy said. "Let the KGB put a guard at my door; it's not important. If I go up to the Supreme Soviet as a deputy, that's fine too. I get used to new conditions rather quickly. This country has always been full of unexpected things." Perhaps most important for the Soviet Union -- which is now suddenly desperate for reliable, objective scholarship on the Soviet past -- Roy has won permission to publish his work here. It is coming out at an astonishing rate. Nearly every serious publication seems to contain his writing: a profile of Khrushchev in retirement, an analysis of Stalin's purges, a piece on Brezhnev's corruption and increasing dementia. Other Soviet historians will be a long time in catching up. Zhores' works on science have already been excerpted in Book Review, a literary weekly, and the biographies he wrote with Roy and on his own -- including "Gorbachev" -- are being prepared for publication. Gorbachev has discovered that Brezhnev's "enemies of the people" are invaluable to perestroika. Sakharov has become his loyal opposition -- and the Medvedevs his most essential historians. "Until 1987 in this country, history was covered up," Roy Medvedev said. "And so the profession itself was devalued, cheapened, degraded." But for his "Let History Judge" and Solzhenitsyn's "The Gulag Archipelago," precious few writers had both the intellectual and moral resources to defy the censors and the police. Even now, from thousands of miles away, the Medvedevs help each other on their various projects. Through the mails, and sometimes with the help of intermediaries, they continue a relationship that is at once scholarly, practical and familial. For Zhores' book on Soviet agriculture and his biographies of Gorbachev and Yuri Andropov, Roy sent him dozens of clippings from the Soviet press and letters packed with advice. Zhores supplies Roy with Western books, handles his foreign-language publishers and, nearly as important, sends to Moscow simple items of the trade that are impossible to find in the Soviet Union: Scotch tape, manila envelopes, folders, a cassette recorder. Roy looks after Zhores' son, who stayed behind in the Russian city of Kalinin. The two men even wrote together via the mails a short, seamless memoir for Family and School, a liberal monthly journal on social issues. "It's uncanny how we share our lives and our experiences. Even from this distance I can always imagine Roy's feelings, how he'll react to various events in our lives," Zhores said. "I think I understand him better even than I understand my own wife, Rita. When something happens to Roy, I personalize it, as if it's happening to me. And I know the reverse is true. When I was sitting in that mental hospital, I could count on Roy to do things on my behalf exactly as I would have wanted." The similarities between the two men are extraordinary, and their habits have not diverged much in their years apart. They are as organized as small-town librarians, having learned the art in communal apartments. Roy's fifth-floor apartment on Dybenko Street is a meticulous arrangement of books and files, a masterly use of space imposed by necessity. File cards stick out of the shelves announcing sections and authors. Zhores, who lives in the middle-class Mill Hill section of London, has arranged his own house in similar fashion. But to arrive at Mill Hill is really to arrive at Dybenko Street. Except Zhores says "hello" at the beginning of an interview and Roy, who speaks German but not English, says "privyet." Each man keeps a photograph of the other nearby. And above their desks, in Moscow and London, there are photographs of a handsome Soviet military officer who died just short of his 40th birthday on the wastes of Kolyma: Alexander Medvedev. In the months after the arrest of their father, the boys and their mother received a series of letters from Kolyma, a notorious region of prison camps in the mining lands of the Soviet far east. Some of the letters from their father were addressed to the Communist Party Central Committee, the Supreme Court, the NKVD. They all protested his innocence, describing in clinical detail various tortures and listing the names of his abusive guards. Like so many women of the era, Roy and Zhores' mother (herself a German Jew) spent days waiting on lines to see government officials who ignored their requests for appeals and information. At home, she railed against Stalin, and the boys were frightened that the neighbors would hear her and turn her in as another "enemy of the people." "There was always the sense that this was odd, a mistake that could not have happened to us," Zhores said. "Of course everyone in the country, when it touched them, felt that way." Roy and Zhores had idolized their father. He had been a strict teacher and a scholarly example to them, urging them to read everything from Jack London to Alaskan adventure stories to Russian classics. His letters from Kolyma betrayed none of his own suffering. They concentrated instead on the boys' future: "My dear Roy and Res: "At last spring has come, a rare guest in this part of the country. I am very far from you, but in my thoughts and heart, I am very close, closer than ever. You fill my everyday thoughts, and you are the aim and essence of my life. "You are on the threshold of becoming young men in the prime of life. I so want to be beside you and give you all my experience and deliver you from youth's mistakes. But destiny has decided otherwise. I do not want my absence from your lives to sadden your youth. "The main thing is that you must study persistently and not limit yourselves just to the school program. Use your time when your perceptiveness and memory is especially keen. Try to be disciplined in your work, for even a mediocre man can accomplish much if he is disciplined. "You are talented, capable boys. you must learn to think and be well organized. What you need above all is patience. You must learn to surmount difficulties no matterhow large. I am sorry for the preaching tone ... "Love, your father." The Medvedev boys were close, but after a while they went to separate schools. "So we would know who we were," Zhores said. For the first 12 years of their lives, they lived in Leningrad, a relatively privileged city with decent food and transportation. After the arrest they lost their apartment at the institute and were forced to move, from Tbilisi to Rostov-on-Don and elsewhere. The family continued to send warm clothes and tinned food to Kolyma, always hoping that it would somehow help Alexander Medvedev. "We didn't feel hatred for Stalin. The main thing was the feeling of being a threatened species in a hostile environment," Zhores said. "The need to struggle and survive was foremost. The mentality was purely biological, purely animal. You needed to find a way to adapt, and the only way for us, as children, to survive was to get the best marks in school, because that meant better treatment. And as half-Jews, we also felt the threat of the Germans. We felt we needed to be ready for anything." In early 1941 came the first sign that the end could be near. The family received a letter from Alexander saying he was in the hospital and could they send vitamins. A few months later, a letter sent to the camps with 50 rubles came back unopened and stamped: "The money is returned on account of the death of the addressee." The boys wept, and their mother spent days in bed not sleeping or eating. For a while she would not accept the worst and continued sending letters and packages of food and clothing. They all came back with the same ominous stamp. Years later, when Roy was interviewing camp survivors from Kolyma for "Let History Judge," a woman called him at home. "Are you the son of Alexander Medvedev?" she asked. When Roy said that he was, he was invited to visit her at her Moscow apartment, which she shared with several other survivors from Kolyma. There, for the first time, he heard the story of his father's death, how he had hurt his arm in an accident in the copper mines and was sent to work in a greenhouse. He developed cancer and was put in the hospital. His fellow inmates knew he was dead only when they saw the camp foreman walking around in the formal suit that Alexander Medvedev had carried with him to Kolyma. "Don't be a philosopher or a historian," Roy Medvedev's mother told him 45 years ago. "In this country, it's too dangerous." But that was the idea for both Zhores and Roy -- to follow in the scholarly, if perilous, footsteps of Alexander Medvedev. In fact, when he arrived at Leningrad State University in the 1940s, Roy undertook a kind of personal historical research. From a distance, he began to study his father's chief betrayer. In 1937 and 1938, the height of the great terror, Boris Alexandrovich Chagin was both a military officer and an agent in the NKVD. He wrote numerous slanderous letters that helped send many men, including Alexander Medvedev, to their deaths. When Roy arrived in Leningrad after the war, Chagin held a prestigious chair in dialectical and historical materialism in the very department where Roy was studying. Zhores, who was studying biology, later discovered the mind of his father's tormentor in the card catalogue at the Lenin Library. Chagin and other academics, it appeared, had taken all the listings of their old ideological tracts out of the library. But it was clear that Chagin had risen to his chair of honor through the ruthless elimination of his rivals and by publishing such books as "The Struggle of Marxism-Leninism Against Reactionary Philosophy" and "The Struggle of Marxism-Leninism Against the Philosophy of Revisionism." "I felt disdain for him, but not hatred or the desire for revenge," Roy said. Chagin, at the age of 90, died in his bed in 1987. The Soviet Encyclopedia contains six sentences about his work, but he never won admission into the Academy of Sciences. Now, when Zhores looks at the portrait of his father above his desk in London, he thinks how he and his brother passed their 40th birthdays long ago, how they have lived through threats, persecutions and all the rest, but, unlike their father, survived to do their work and even to see it published in the Soviet Union. "We are lucky sons," Zhores said. In their years apart, the Medvedev brothers have diverged, somewhat, politically. "I'm not like Roy anymore. I'm not a professional political scientist. I have no fixed dogmas," Zhores said. "Roy is a democratic socialist, kind of what you might find in the Italian Communist Party. But eventually I've become disappointed in socialism. I'm not a Thatcher man. In British terms, I suppose I'm a social democrat or a liberal. They'll never win power but I sympathize with them. "A normal capitalist system is better designed to create a consumer society, it seems to me. Soviet society is not designed to satisfy consumption, but rather to satisfy certain cultural questions. I think Roy thinks this, too, but he won't acknowledge it." Thousands of miles to the east, in his dim, orderly study, Roy Medvedev was preparing for the opening of the Congress of People's Deputies. Without his asking for it, the Communist Party restored his party card after taking it away in 1969. The state also provided a last sweet surprise: "Two days before the March elections, the KGB sent me the archives and books they had taken from me 14 years ago," Roy said. Among them were books by Solzhenitsyn and papers of Trotsky, dozens of letters, notes written to Sakharov, the manuscript of the book "A Question of Madness" written with Zhores, a manuscript describing the extent of fraud in the novels of Nobel Prize-winning novelist Mikhail Sholokhov. "There are a lot of treasures, and it looks like they took rather nice care of them." Roy Medvedev said that at the congress, his first order of business would be to demand that all exiles be permitted to visit or, if they choose, return for good. "I owe that much to a lot of people, especially to my brother Zhores." As a scientist and a citizen, Zhores Medvedev does not want to leave England for good but in July he will visit Moscow and, for the first time in 16 years, be reunited with his twin. He will lecture on the dangers of nuclear power. Roy Medvedev has been invited to a December historical conference in San Francisco. It will be his first trip abroad.