IN NOVEMBER 1935, a 19-year-old American under-graduate at Cambridge University wrote his mother a remarkable letter. He was probably pleased at the time with the degree of insight it showed into his own character. He can have had no inkling of how prescient it now seems. For what he was telling his mother, without knowing it, was that he had been visited by the kindly ones. These furies were to pursue him the rest of his life.

He had spent the evening, he told his mother, with his friend James, "and Whitney's friend Guy Burgess and an art historian called Anthony Blunt." He added: "Now at half past eleven I sit here and try to describe the terrible significance of it all."

Terrible its significance certainly turned out to be for him. His mother already knew that he had become a communist at Cambridge. That would in any case not have shocked her. What he was trying to explain in this letter was that he was less of a communist than he seemed. "My actions," he wrote, "are based on my personal needs rather than my convictions." He had been afraid, after the breakup of a love affair with a girl at school, "that I'd become incapable of loving. Now I've learned that I'm able to love the communist students, even if I don't love communism itself."

The young man was Michael Straight. His mother, Dorothy, was a Whitney, an heiress out of the world of Henry James' novels. After Michael's father died on active service in World War I she turned to good works, to the left, and to what would now be called radical chic. She was a prototype--it would no doubt be unfair to call her a caricature--of the wealthy woman of good causes. She was an enthusiast for labor unions and settlement houses, for socialism and feminism and pacifism. She led a march down Fifth Avenue in aid of votes for women. And she put up the money for The New Republic.

Then she married a young Englishman called Leonard Elmhirst, as idealistic if less wealthy than herself. They bought Dartington Hall, a Tudor manor house in an exquisite fold of the green Devon hills, and turned it into what it remains today, an experimental school and a center of world importance for music and the arts. It was a utopia for those who after World War I dreamed of a new society liberated by the arts; in the late 1920s, that was a revolutionary dream.

When it was time for Michael to leave Dartington, what more natural than for his mother to consult Felix Frankfurter? What more likely than that Frankfurter should recommend a year under his friend Harold Laski at the London School of Economics?

The school's reputation as a hotbed of radicalism has always been exaggerated. But there were radicals there in the 1930s, as there have been since. In the 1930s, as in the 1960s, they were concerned both about the school's internal democracy, or lack of it, and about international affairs: specifically, in the year 1933-34, when Michael Straight was there, about the rise of Hitler.

Straight's friends at LSE were radicals, some of them communists. What more natural than that, when he moved on to Cambridge to read economics at Trinity, he should move into a circle of radicals, some of them, too, communists.

Straight was a bright student, and he studied with some of the great names in 20th-century economics: D.H. Robertson, Joan Robinson, John Maynard Keynes himself. But it was the communists who had the most influence on him, and it was political activism, not theory, that excited has interest.

Specifically the three chief influences were Maurice Dobb, James Klugman, and John Cornford. Dobb was and is an eminent Marxist academic economist. Klugman went on to be a committed bureaucrat of the Britsh Communist Party. And John Cornford was a romantic, gifted and attractive young poet, born into the heart of Cambridge's elite. All his family were brilliant dons, his mother a granddaughter of Charles Darwin.

Straight became active among the Cambridge communists, though he had reservations. He was reluctant, for example, to have it known outside Cambridge that he was a communist. "Students like myself," he writes now, in what sounds like honest recollection of past self-deception, "owed no allegiance to the communist party itself. We had enlisted as students in response to extraordinary individuals and without them were adrift."

Straight became a member of the Cambridge Conversazione Society, known as the Apostles, the secret society that chose young men for their intellectual brilliance, sometimes for their intellectual family connections, and often for their homosexual predilections. (Not Straight: his sexual preference has always been for women. Like name, like nature!)

It is too simple to say that the Apostles had become a recruiting agency for Soviet intelligence. But a number of those who became Soviet agents like Burgess and Blunt were members. And perhaps the atmosphere of the Apostles, the slightly bogus intellectualism, the clandestinity, the smart leftism, and the sense of superiority to bourgeois prejudices, subtly preconditioned ambitious young men, shocked by what they saw as the heedless conservatism of their own society, to what can now only be called treason.

It was John Cornford whom Michael Straight most admired. It was the news of Cornford's death, killed fighting for the left in Spain, that led to his downfall.

To explain, perhaps to excuse, his decision to work for the Soviet Union, Straight cites Joseph Conrad's novel Under Western Eyes. In it the student Razumov is suddenly confronted in his room by Haldin, an older student, who has just assassinated an odious czarist minister. Haldin asks Razumov to help him escape. "No great matter, that.""Razumov agrees, but then betrays Haldin. Straight comments, Razumov "has lost his independence. He can never again call his life his own."

It was Anthony Blunt--the elegant art historian, homosexual, apparently effete, but in reality as hard as nails--who turned the screws on Straight. He ordered him, on behalf of Soviet intelligence, to fake a breakdown and a change of political allegiance as a result of Cornford's death, to use his family contacts to get a job on Wall Street, to go underground. To become a mole. No great matter.

Straight struggled, but he accepted. He appears to have thought at the time, perhaps thinks now, that he had no choice. He did not go to Wall Street, but her did return to America. He got a job, unpaid, writing reports for the state department. Later he worked as a speechwriter for Benjamin V. Cohen and Thomas G. Corcoran, the legendary New Deal operators. He went to all the right places, shared a house with Joseph Alsop, met all the right people. In New Deal Washington, as in left- wing Cambridge, all the doors were open to a radical Whitney.

Then one day there was the phone call. From a young man with a European accent who telephoned to say he brought greetings from the friends in Cambridge. They met. The mystery man, who called himself Michael Green, asked Straight to hand over documents. Straight said nothing interesting crossed his desk.

Straight's story is that he handed over no restricted information to Green or to any other Soviet agent. In view of the fact that he has not been prosecuted, quite aside from the general honesty of his confession, I believe him. Instead, on four or five occasions, he says, he handed his control a little essay on the errors of Soviet policy. All contact with "Michael Green" ended in 1942.

His difficulty was, as the puts it, that he was no longer, perhaps had never been, a committed communist; yet he was unwilling to reject the ideals of those of his friends who were. "I was not able to repudiate John Cornford and my own past in Cambridge," as he puts it. "Nor was I willing to be a Soviet agent in the Department of State."

Straight solved his problem by leaving the government for good and going to that family estate, The New Republic. He became editor, and played an important part in the politics of the American left immediately after World War II. In particular, he was closely involved with Henry Wallace. Historians will find his account of the Soviet efforts to influence Wallace and his third-party movement an important corroborative source. His conclusion is that the third-party "Wallace for President" movement was Soviet-influenced. "Through my association with Henry Wallace, I was being drawn towards the Soviet orbit," and that was somewhere he did not want to be. Throughout the years when the House Un-American Activities Committee terrorized Washington, Straight lived in fear. Strangely, his name was never named, though he was involved in the fight to vindicate others, such as Owen Lattimore in 1954.

In 1949--it is like an implausible scene from a novel, but I am sure it is true--Straight was back in England on family business when he met Guy Burgess, the "fallen angel" of the Apostles, in Whitehall. Burgess said the Apostles were to hold their annual dinner in a Pall Mall club that very night. The next day Burgess and Blunt cornered him, avid to find out what he was going to do.

"Are you still with us?" Burgess asked.

"You know that I'm not," Straight answered.

"You're not totally unfriendly?"

"If I were," Straight replied, "why would I be here?"

It was, Straight himself comments, a "weak, evasive answer."

It was. And it is hard to avoid the judgment that Straight's behavior over the next third of a century continued to be weak and evasive.

He did finally decide to come clean, but only when he was offered a job by the Kennedy administration as chairman of the federal arts council. He talked to the FBI, and they asked him to talk to MI5, the British counterespionage security service.

To his amazement, he found that he knew more about Burgess and Blunt than anyone MI5 had yet interviewed. They asked him to confront Blunt, and he did so.

Evasively, he said it was his love of the arts that made him talk. "We always wondered how long it would be before you turned us in," said Blunt coldly.

There is something pitifully unsatisfactory about the way Straight describes his further cooperation with the British authorities. He rationalizes, he sentimentalizes. He hopes that he cleared more people than he implicated. And so on. He seems unaware of the inconsistency between the contempt he expresses for those who talked to the House Un-American Activities Committee, and the satisfaction he felt when he talked himself. The truth, I would guess, is that the psychological relief of getting it all off his chest after so long was irresistible.

It is a sad story, a sad book. It is the story of a man born with great gifts, boundless opportunities, a good heart and a good mind, lacking only the horse sense to see through a pile of claptrap and the guts to tell a transparent Iago like Anthony Blunt to go and boil his head.