The perjury trials of Alger Hiss in 1948 and 1949 were the courtroom blockbusters of their day.

Whittaker Chambers, a senior editor at Time magazine, had accused Hiss, once a rising star in the State Department and in 1948 the newly appointed president of the Carnegie Foundation, of giving Chambers secret government documents to pass on to the Soviet Union. Hiss denied the charge under oath both to the House Un-American Activities Committee and to a federal grand jury.

(Because the acts were alleged to have taken place more than a decade earlier, neither man could be tried for espionage. The statute of limitations had expired. )

The Hiss case came at a time when the temperature of relations between the United States and its former World War II ally, the Soviet Union, was plummeting to Cold War levels. The congressional investigation of Hiss brought to the fore an aggressive young congressman named Richard M. Nixon and set the stage for Sen. Joseph R. McCarthy's later efforts to ferret out supposed communists in government ranks. For years, conservatives would continue to attack Hiss and liberals would argue that he had been railroaded.

In this engrossing, thoroughly researched biography, Sam Tanenhaus profiles Chambers, the man whose accusation of Hiss kicked over the ant hill.

Chambers had testified before a federal grand jury (and the House Un-American Activities Committee) that - at a time when Chambers was a member of the Communist Party - Hiss had provided him with official documents that Chambers then microfilmed and passed along to Soviet agents.

Hiss at first denied even knowing Chambers, but then admitted he may have known him as George Crosley, a journalist down on his luck in Depression-era Washington. As for the charges about passing along documents, Hiss denied them.

Federal prosecutors filed two counts of perjury against Hiss, charging that he had lied to the grand jury, first, in saying that he had not seen Chambers after Jan. 1, 1937, and second, in denying that he had transmitted documents to the former communist.

Superficially, the two antagonists - Hiss tall and handsome, imperially slim and impeccably attired, Chambers short, dumpy and disheveled - seemed utterly unalike. But beneath the surface, as Tanenhaus shrewdly notes, the two had a lot in common. Both had attended Ivy League schools - Hiss Harvard, Chambers Columbia. Both came from middle-class families of modest means and both had weathered grievous family misfortunes: Chambers' younger brother and Hiss' father and sister had committed suicide. In history, of course, the two have been joined forever, but Tanenhaus has wisely resisted the temptation to write a dual biography.

Hiss may not have known Chambers as George Crosley, but he certainly didn't know him as Whittaker Chambers. The name Chambers said he used in dealing with Hiss was Carl Carlsen, one of many names Chambers, who was born Jay Vivian Chambers on April 1, 1901, assumed throughout his life. He didn't become Whittaker Chambers - Whittaker was his mother's maiden name - until he began working for Time in the early '40s.

The man was a born outsider, the pudgy, lonely child of an artist father whose homosexuality - in that less-tolerant era - was an ongoing cause of embarrassment and a mother whose yearning for respectability was continually thwarted by her husband's bohemian ways. Chambers' maternal grandmother, who lived with the family, drifted from eccentricity into madness. Often, she would stand outside their house and loudly denounce her son-in-law's ``depravity. ''

Chambers joined the Communist Party in 1925, withdrew from active participation for a while, then took up the cause with renewed passion in 1931, becoming editor of the New Masses, the party's literary journal, the following year. Shortly thereafter he was ordered to go underground and for the next several years commuted between Washington and New York bearing microfilmed copies of government documents. Eventually, however, certain worrisome developments - among them the Moscow trials, the Soviet-led purge of Loyalists in Spain, and the unhappy fate of several of his underground colleagues - prompted Chambers to defect.

Tanenhaus' account of how Chambers did this - moving first to Florida, then to rural Maryland, a rifle or revolver always within easy reach, even when he slept - is as exciting as any episode out of John le Carre. But it's the hearings and the trials, naturally, that form the centerpiece of his narrative. Given the immense amount of material - thousands of pages of transcripts recording millions of words of testimony - Tanenhaus' summary proves a model of how to go about selecting and arranging pertinent details.

The first trial ended in a hung jury, which had been the aim of Hiss' trial lawyer, Lloyd Stryker. But Hiss dropped Stryker for the second trial and ended up being found guilty.

The affair proved to be the climax of both principals' lives and careers. Chambers retired to his Maryland dairy farm and wrote his autobiography, Witness. The book, which was generally well-received by critics and topped the best-seller lists, is one of those books, Arthur Koestler said, ``which, if they had remained unwritten, would leave a hole in the world. ''

Ever the misfit, Chambers never quite saw eye-to-eye with his anti-communist admirers. He kept his distance from McCarthy, correctly predicting that the Wisconsin senator's recklessness would eventually give anti-communism a bad name. And he displayed a fine regard for civil liberties. ``The spectacle of an artist like Paul Robeson,'' he wrote, ``denied a passport by his own government, makes us traduced of other nations. '' When certain conservatives objected to Hiss' being given a passport, Chambers told reporters: ``Alger Hiss is an American citizen. He has every right to apply for and receive a passport. ''

Chambers, who had suffered from heart problems since the early '40s, died of a heart attack in 1961.

As for Hiss, who died in November, four days after his 92d birthday, he served 44 months of a five-year sentence in the federal penitentiary at Lewisburg, Pa. Upon his release, he remarked dryly - one might even say sagely - that ``three years in jail is a good corrective to three years at Harvard. '' To the last he insisted that he had been wrongly convicted.

In 1992, Russian Gen. Dmitri A. Volkogonov announced that a search of KGB files offered no evidence that Hiss was ever a Soviet spy. But some weeks later the general admitted that the search had been cursory, that many files had been destroyed and that he could not, in any event, speak for other Soviet intelligence agencies. Moreover, evidence for Hiss' involvement did turn up in communist archives in Hungary. Then, in 1993, declassified State Department documents indicated that a security investigation in 1946 had revealed that Hiss had procured top secret reports - on atomic energy and China policy among others - that he was not authorized to see. Finally, a Soviet cable dating from 1945 made mention of a Soviet agent in the State Department who had attended the Yalta Conference - as Hiss had.

It is hard not to conclude that Harry Truman, who initially dismissed the matter as ``a red herring,'' was on the money when he later said of Hiss to Dean Acheson that ``the s.o.b. . . . is as guilty as hell. ''

So why did Hiss persist? Tanenhaus thinks that even Chambers, who portrayed Hiss as ``a principled revolutionary, nearly heroic in his dedication to the great cause,'' failed to take the proper measure of the man. ``The salient fact of Hiss' career,'' Tanenhaus observes, ``was not self-sacrifice but opportunism. '' (Hiss' wife, Priscilla, later spoke bitterly of her husband's willingness ``to sacrifice other people, including me,'' for his vindication. ) As Tanenhaus sees it, Hiss' aim was simply to preserve ``an endangered reputation. ''

Still, to many, Hiss was a martyr and Chambers a pariah. As Chambers noted in Witness: ``No feature of the Hiss case is more obvious, or more troubling . . . than the jagged fissure . . . between the plain men and women of the nation, and those who affected to act, think and speak for them. It was . . . in general the `best people' who were for Alger Hiss . . . the enlightened and the powerful . . . who snapped their minds shut. . . . ''

In attempting to explain ``this curious disjunction,'' Tanenhaus cites critic Leslie Fiedler, who traced it to ``the implicit dogma of American liberalism'' that in any political drama ``the liberal per se is the hero. '' The Partisan Review's Philip Rahv put it more bluntly: The pro-Hiss faction ``fought to save Hiss in order to safeguard its own illusions. ''

Frank Wilson is an Inquirer copy editor.