September 15, 2002 By DAVID A. HOLLINGER J. Robert Oppenheimer was once much closer to the Communist Party than he ever admitted. Yet as director of the laboratory that built the atomic bomb and as a weapons adviser to the government after World War II, he served his country more scrupulously than did many of those who made an issue of his loyalty. This arresting paradox is at the heart of the most commanding history yet written of the internal politics of the United States during the early years of the nuclear age, ''Brotherhood of the Bomb,'' by Gregg Herken, a historian at the Smithsonian Institution. Herken shows how high-ranking officials conspired, sometimes with illegal wiretaps, to push Oppenheimer out of government service in 1954, and forced an Army general to testify falsely that Oppenheimer was a security risk. He also shows that Oppenheimer's petty deceits about who told him what concerning potential Soviet espionage were motivated more by personal than political loyalties and damaged himself more than anyone else. Herken's new material includes recently opened F.B.I. files, more than 80 interviews, and previously closed papers of several key actors in the drama. The ''brotherhood'' of his title has a double meaning. It refers to the men in the subtitle, ''The Tangled Lives and Loyalties of Robert Oppenheimer, Ernest Lawrence and Edward Teller.'' These giants of atomic physics were bound together for decades in complex, tension-ridden alliances partly of their own making, but often created by military and political institutions that used them. Their ventures were driven by vanity, political dogma, vested interests, lust for power and, most shocking, perhaps, honest assessments of the welfare of the nation and the world. But Herken's title also invokes the relationship between Robert Oppenheimer and his brother, Frank, also a physicist, whom Robert brought into the Manhattan Project despite Frank's having been a member of the Communist Party from 1937 to 1941. Later, Robert Oppenheimer's contradictory stories about spies appear to have been designed to protect his brother. These lies made him vulnerable to attack by those who wanted to destroy him for other reasons, especially for opposition to specific weapons initiatives supported in the early 50's by Teller and the Air Force. Teller, who eventually replaced Oppenheimer as the nation's most influential adviser on nuclear weapons, testified in 1954 that Oppenheimer should be denied a security clearance. Herken tells the stories of both brotherhoods simultaneously in an enthralling narrative that moves from Berkeley to Los Alamos to Washington and several other places where bombs were designed, tested and debated. The University of California, Berkeley, was the academic home of both Oppenheimer and Ernest Orlando Lawrence, a machine-designing experimentalist of enormous creativity who had won a Nobel Prize in 1939 for designing the cyclotron. Lawrence was the government's initial choice to direct the Los Alamos laboratory. But his casual attitude toward security gave pause to James B. Conant and Vannevar Bush, the top science advisers to the White House. Lawrence had brought Oppenheimer into a committee of scientists advising the government about building the bomb, and he offered such shrewd advice on one technical question after another that he became indispensable to the project. Gen. Leslie Groves, the military officer in charge of the Manhattan Project, ultimately chose Oppenheimer, even though he was a theorist with no administrative experience, as director at Los Alamos. Groves was aware that Oppenheimer's family, friends and students included many former members of the Communist Party, but his own contact with Oppenheimer in 1942 convinced him of his integrity and loyalty. Yet Herken's research places Oppenheimer closer to the Communist Party in 1940 and 1941 than even the F.B.I. was able to do during its intensive investigations in the 40's and 50's. Herken leaves open the possibility that Oppenheimer was a member of the party's secret ''professional section'' in Berkeley. He is more decisive on a much more important issue: he finds no evidence that Oppenheimer ever passed secret information to Soviet intelligence, or that any sympathy with Soviet political aims distorted the advice he gave the American government. There certainly were spies at Los Alamos. Klaus Fuchs and Ted Hall have long since been identified, and there was at least one other whose identity remains undisclosed. But F.B.I. wiretaps quoted by Herken reveal Robert Oppenheimer's Communist friends in Berkeley plotting espionage while complaining ruefully about his refusal to talk to them about his secret work. Soviet documents available since the end of the cold war record frustration that agents had not been able to recruit Oppenheimer. Herken shows that Oppenheimer, once he entered government service, vindicated Groves's faith in him. Groves was coerced into testifying against Oppenheimer in 1954. The episode is one of many recounted here that reveal the paradox of Oppenheimer's loyalty being made an issue by people less scrupulous than he was in the exercise of their duties. The basis for what amounted to a kind of blackmail was a conversation between Groves and Oppenheimer late in 1943, which made Groves vulnerable to prosecution for felony violation of a statute prohibiting withholding of material information about espionage in wartime. The general ordered Oppenheimer to name physicists who had been approached by Soviet agents. Oppenheimer himself had alerted junior security officers that overtures had been made, but declined to identify the physicists who had been targeted as potential spies. Now he told Groves that there was only one -- his brother, Frank. But he extracted a promise that Groves was never to disclose this to the F.B.I. To the F.B.I. Oppenheimer gave yet another account of the espionage effort, making no mention of his brother, but implicating others, including Haakon Chevalier, a Berkeley professor of French who, Oppenheimer said, served as an intermediary in the Soviet initiative. Groves not only kept his promise, but was a steadfast defender of Oppenheimer for the next decade, voluntarily giving Oppenheimer in 1950 a resounding written testimonial he could show to any authorities that questioned his loyalty. But back in 1943 an aide in whom Groves confided had leaked the Groves-Oppenheimer secret to the F.B.I. During the intervening years J. Edgar Hoover was furious at Groves for keeping from him what he already knew privately. So when Lewis Strauss, chairman of the Atomic Energy Commission, prepared A.E.C. hearings on Oppenheimer in 1954, Hoover was ready to help. Most of the evidence against Oppenheimer was information long on record about his associations with Communists, and his conflicting stories about the role of his friend Chevalier. But Strauss and Hoover knew that this old information might play differently if Groves could be induced to put a different construction on it. Hoover worked closely with Strauss to orchestrate Groves's testimony in the context of Groves's vulnerability to prosecution. He was allowed to avoid mentioning his private conversation with Oppenheimer. Thus he was not obliged to contradict testimony Oppenheimer gave at the same hearing to the effect that his brother Frank had ''nothing whatever to do'' with the approach made by Soviet agents. All Strauss needed on the record from Groves was a clear statement that he now regarded his protege as a ''security risk.'' Groves delivered on cue. Did Oppenheimer tell Groves the truth? And if so, might Oppenheimer's reluctance to see his brother branded as someone whom his Communist friends found to be good spy material have been based on awareness that his brother was, indeed, tempted? Herken did not find evidence to support an answer to these questions. But ''Brotherhood of the Bomb'' enables us to put what we do not know in the perspective of what we do know: 35 years after his death, J. Robert Oppenheimer remains, more than ever, one of those people who, in Stephen Spender's phrase, ''leave the vivid air singed with their honor.'' David A. Hollinger is Preston Hotchkis Professor of History at the University of California, Berkeley. Copyright 2003 The New York Times Company