In a lengthy interview at his home in Kiev, the 69-year-old son of Stalin's infamous henchman claimed that Robert Oppenheimer, the scientific director of the United States' Manhattan Project, made a secret visit to Moscow in 1939, six years before the US exploded the world's first nuclear bomb. 'At that time I did not know it was Oppenheimer. He was a young man who lived in our house and slept in my room,' said Sergo Beria, himself a scientist who was arrested after his father's downfall in 1953 and banished from the Russian capital. 'He had another name. He came through France; French comrades helped him to get here, but he was very sorry to leave without any result. He wanted to work at the project here in the Soviet Union.'
The claim that Oppenheimer stayed at Beria's mansion off the Moscow Ring Road comes amid heated debate in Russia and the United States over who deserves credit for the development of the Soviet Union's first atom bomb, exploded in the deserts of Kazakhstan in August 1949.
According to Sergo Beria, Oppenheimer was never recruited as a spy but, at a time when neither Britain nor the US had a nuclear weapons project, had come to Moscow because of concern that Hitler might become the first to harness nuclear physics for military purposes.
A leading American scholar of the Soviet nuclear programme, David Holloway, doubts that Oppenheimer was ever Beria's houseguest: 'Bizarre things happen but this seems very unlikely.' Speaking by telephone from Stanford University, he said: 'It seems a continuation of an old battle between the KGB and physicists. There has always been deep resentment (in the secret service) that they did not get the dachas, the red banners, the medals, or if they did that they were not allowed to wear them in public.'
Lavrenti Beria, Stalin's right- hand man in Moscow from 1938 until the Soviet dictator's death in 1953 and his own execution, was put in charge of the Soviet nuclear drive after the US annihilation of Hiroshima. He was made head of an eight-man 'Special Committee on the Atom Bomb'. Scientists and spies immediately began feuding. Pytor Kapitsa, the greatest Soviet physicist, wrote to Stalin complaining of Beria senior's brutish ignorance. Beria retaliated by having Kapitsa dropped from the programme. Beria's son, Sergo, was only a young man at the time but became involved in the Soviet drive to become a nuclear power, working as a rocket-design engineer at the so-called Construction Bureau No 1 in Moscow.
Sergo's decision to speak out follows the publication of controversial memoirs by one of his father's former underlings, a retired spy, Pavel Sudoplatov, 87. The work has been widely denounced for its claims that Oppenheimer and three other prominent physicists, including the founding father of modern physics, Niels Bohr, helped Soviet intelligence steal America's bomb-making secrets and thus pave the way for the first Russian bomb. This goes far beyond the well-documented treachery of Klaus Fuchs and several other relatively minor figures.
Ten of Russia's leading scientists issued a joint statement in Moscow last week condemning 'provocative attempts by reactionary, anti-democratic, anti-reform and anti-intellectual forces in Russia to discredit the . . . achievements of Soviet scientists working on the nuclear project and present them as blind imitators working from cribs obtained by intelligence.'
Sergo Beria disputes details of Mr Sudoplatov's account of massive penetration of the Manhattan Project but, unsurprisingly, sides with his father and other Soviet spies in the increasingly bitter and public battle for recognition: 'They (the scientists) were not agents, but they wanted this technology to come to Russia. First they were afraid that Germany would realise the project first and then, after the war, they did not want America to have a monopoly . . . They created a situation where information could pass. They did not give it themselves but they wanted to help.'
Oppenheimer, who married a former Communist and whose brother was a former Communist, was mistrusted by many in the FBI and admitted to General Leslie Groves, the military director of the Manhattan Project, in 1943 that 'he had probably belonged to every Communist front organisation on the West Coast'. But there has never been any solid evidence of disloyalty during the Manhattan Project nor of any secret visit to Moscow before that.
Sergo Beria, however, insists such a trip took place: 'It was Autumn 1939, around September. My father told me I could stay at home while he (Oppenheimer) lived in our house because otherwise he would be alone and bored. He would leave each day accompanied by my father's first deputy, (Vsevold) Merkulov.
'But sometimes he stayed at home, and so did I to keep him company. He asked me what we were doing at school, he spoke English with me but he also spoke perfect German.'