CONSPIRACY OF SILENCE The Secret Life of Anthony Blunt By Barrie Penrose and Simon Freeman Farrar, Straus and Giroux. 616 pp. $22.95

IN 1963 Sir Anthony Blunt, director of the Courtauld Institute and surveyor of the queen's pictures, spent the summer term as a visiting professor at Penn State. He was quickly put at his ease, as his students understandingly furnished him with an annotated survey of Centre County bars. Sir Anthony, as someone later put it, ungently, was "not a screaming queen," but beneath his cosmopolite elegance was a compulsion to solicit "rough trade" on the order of his pick-ups in London pubs and public lavatories.

For Blunt it was a successful summer. Before rapt classes he charmed his way across centuries of painting in what would be his last idyllic year. On April 23, 1964, acting on a tip from America, Arthur Martin, an intelligence operative in Britain's MI5, would interview Sir Anthony in his flat overlooking Portman Square and, at the price of immunity from prosecution and official silence, elicit a confession. Blunt had been a Soviet agent since the early 1930s -- the "fourth man" often linked anonymously to the notorious trio of Guy Burgess, Donald Maclean and Kim Philby, spies from the same Cambridge milieu who had disappeared and then surfaced in Moscow. Sir Anthony had assisted Burgess and Maclean's getaway.

Martin and Blunt met about 10 times for debriefing between April and November explaining into an MI5 tape recorder why and how talented and privileged Englishmen -- and women -- had betrayed their country, and continued to betray it, even after the ideal that had motivated many of them had turned sour.

Since young Englishmen with elitist backgrounds and old school ties had the pick of posh Establishment situations, and Russia was not, as some who visited there realized, more perfect than Paradise, their disloyalty to class and country continues to have a mystery and a morbid fascination that eclipses most spy fiction. As one agent recruited out of the working class explained a generation later, "You have to make a time jump and try to imagine what it was like." For the bitter Depression-era child of an unemployed laborer, on an education grant at Cambridge more than twice his father's last meager wages, and whose perception was that flabby and corrupt European democracies were going to appease the Nazis until it was too late to save themselves, there was one kind of gravitation toward communism. For comfortable public school types already drawn into a homosexual subculture, and infused with at least a modicum of Marxist self-guilt, there was the thrill inherent in the excitement and danger of a covert double patriotism -- not to one's own country and to communism, but to the subterranean worlds of male bonding and class betrayal.

E.M. Forster, who had emerged from an earlier Cambridge generation of snobbery, buggery and class guilt, had coined an oversimplification dear to the hearts of his generation and its successors -- that if he had to choose between betraying his country and betraying his friends, he hoped that he would have the courage to betray his country. Oxbridge gentlemen of Forster's time and after populated the interlocking communities of government, university and business. Their credentials and friendships established them as beyond suspicion even when they were scandalously indiscreet homosexual alcoholics, ripe for blackmail or for one of the many varieties of political and sexual seduction practiced by the agencies of espionage. In the years just before World War II, and then in wartime itself, little thought was given to screening candidates for the intelligence services, or the Foreign Office, or for army commissions. A recommendation, or the right school or club, was usually enough. Even a Marxist past was of no consequence. After all, wartime recruiters of talent thought, if they refused to employ young gentlemen with records of university radicalism and homosexuality, who would be left? Inevitably, a conspiracy of silence protected both employers and employed.

What went on behind that porous curtain of silence is the story told, some of it ploddingly, by Barrie Penrose and Simon Freeman. Even though much of the story has been told in earlier books, it remains mind-boggling, for the authors include chunks of new interviews with the principals, and the cast of characters in the played-out drama continues to grow. This book itself, which appeared last year in England, has a new preface and a new, lengthy postscript for the American edition to accommodate the latest allegations. One that has long simmered is that the very wartime and postwar head of MI5, Sir Roger Hollis, possibly unknown even to the Soviet agents in his own organization, was a Comintern mole himself.

ALTHOUGH THE book's subtitle promises a secret history of Anthony Blunt, at least half its pages provide a context for that life in the compulsions to treason of Blunt's generation of gifted young people. Few were serious, doctrinaire communists. Fewer still were poor. Blunt may have been in part rebelling against his foolish, royalty-happy mother and his highflown, stuffy, clergyman father, yet he was equally royalty-fixated, and gave way to none in public pompousness. The Byzantine conspiratorial nature of working for intelligence while covertly working for the Soviets fit well with the frisson of homosexual intrigue in a complementary underworld. Doubling that double life later as leading art historian of his generation in England, persona grata at Buckingham Palace while rough trade had access to his porter-protected eyrie in Portman Square, was Blunt's ultimate ego trip -- until the defections of his friends closed in the walls around him and forced him into 15 years of frightened legal immunity. While he tried to go on with his professional life, and did so with a debonair chilliness that belied his cornered-rat status, he knew that someday someone would talk. Then it would all be over. And someone did.

What the Establishment mentality was like, and why the unmasking took so long, can be encapsulated in the experience of Blunt's old friend, the novelist Rosamond Lehmann, who once tried to inform MI6 that Guy Burgess was an agent for the Comintern. She called its head, Sir Stewart Menzies, whom she had met once socially. Was it about "GB," he wanted to know, deducing from her hints. She said yes. "But he said, my dear, it's Friday. I'm going away for the weekend. I asked if he'd see me on Monday and he said that he was taking his little girl to Ascot. I felt that he was putting me off . . . He ought to have said come at once. But Menzies didn't call back."

Burgess, even more than his friends, of whom Blunt was closest, was indulged beyond any reasonable understanding. More often than not he was dirty, drunk and disorderly; he boasted of buggery and betrayal. Yet he was employed by, or had privy to, intelligence, the Foreign Office, the BBC, and other Establishment bases, and the orders, finally, to pick him up came only when he was making good his escape. Blunt, at the least, had the intellectual and emotional self-discipline, however compartmentalized his lives, to play them brilliantly. Penrose and Freeman conjure up a bizarre -- yet accurate -- image of the later Blunt: "The Surveyor of the Queen's Pictures awaking at the Courtauld after a night with rough trade; then taking seminars with his students, emphasizing the need for art historians to be the champions of Truth and Beauty, before slipping away late in the afternoon for a session with {Arthur} Martin."

Insiders yet outsiders, Blunt and his cronies (many, but not all, homosexual; many, but not all, Oxbridge intellectuals) moved with such impunity within the corridors of power as to suggest either a disintegration of the qualities that had made Britain a great power, or that the accidents of history had once worked to Britain's advantage more than had its brains. Individual penalties could be painful -- exile, isolation, shame, the revoking of rewards. Blunt had his knighthood withdrawn in 1979 -- not when he confessed, but when he was exposed. When he died in 1983, he was a shattered man, afflicted with cancer, shunned by most of his surviving friends, bereft of honors fairly earned. Although other conspirators suffered occasional alarms or embarrassments, most lived out their days -- and nights -- in distant comfort from the Soviet utopia they had, for one reason or another, served.

Stanley Weintraub, Evan Pugh Professor of Arts and Humanities at Pennsylvania State University, is the author, most recently, of "Victoria: An Intimate Biography."