Mr. Philby, who never wavered in his loyalty despite Moscow’s 1939-41 pact with Hitler and the invasions of Hungary in 1956 and of Czechoslovakia in 1968, was long regarded as a hero in the Soviet Union, which hailed him as a committed Marxist, put his face on a postage stamp and buried him in the Kuntsevo cemetery in Moscow along with other Soviet heroes, including the secret police agent who murdered Leon Trotsky.

One of the documents on display, however, hints at the suspicion and distrust that greeted Mr. Philby when he first fled to Moscow in 1963, slipping out of Beirut, Lebanon, aboard a Soviet ship bound for Odessa. The partial transcript of a 1977 speech he gave to K.G.B. officers in Moscow records Mr. Philby saying: “It is the year of my first visit to the Soviet intelligence headquarters. It has taken me a long time to get here.”

Christopher Andrew, a Cambridge University professor and the author of classic books on Soviet espionage, said Mr. Philby had to wait 14 years after his arrival in Moscow before being received at the intelligence headquarters “because they didn’t trust him.”

Mr. Lyubimov, the former K.G.B. officer, said this was not true, explaining that Mr. Philby had fallen under suspicion among members of Stalin’s intelligence service during World War II but “was completely trusted” once he got to Moscow in 1963. Mr. Lyubimov also disputed widespread accounts by witnesses of Mr. Philby being drunk and despondent in Moscow. “When he first came to Russia, because of the shock of the whole affair, he was just drinking but this did not continue a long time,” Mr. Lyubimov said.

All the stolen British documents put on display — marked in red with the words “Top Secret. To be kept under lock and key. Never to be removed from the office” – relate to World War II. Most are reports on intercepted messages sent to Tokyo by Japanese diplomats on the state of the German military and other secret matters. They include a report by a Japanese envoy in Italy on Mussolini’s account of how Hitler had sustained “minor injuries” and had his hair burned during a failed assassination attempt in East Prussia in July 1944.