<i> Ssshhhh!</i> : THE CATCHER WAS A SPY: The Mysterious Life of Moe Berg, <i> By Nicholas Dawidoff (Pantheon: $24; 453 pp.)</i>

“People think I’m making him up,” says Linda McCarthy, and with good reason. McCarthy is curator of the CIA Museum. Her license plate reads MOE BERG. She “idolizes” him, she says. When Berg died, a lot of people were obsessed with him. Some still are. His name keeps coming up.

Who was Moe Berg? He may have been 90% genius, 10% fraud. It may have been the other way around. But this we know:

He was a major-league catcher.

He was a spy for wartime OSS, poised, at one critical juncture, to blow away no less a man than Werner Heisenberg.

He was exceptionally learned, conversant with a dozen languages, with physics, opera, Petrarch’s sonnets and the trajectory of a screwball.

He was weird. Very, very weird.

In the lucid, literate, endlessly compelling “The Catcher Was a Spy,” Nicholas Dawidoff has parsed the paradox, taken it apart and put it together again as well as any writer could. Elements of the puzzle are missing, and always will be: Of necessity, the surface of spies’ lives are cratered with caesurae, with discontinuity, with mystery, and Berg was as mysterious as they come, even--especially--when he didn’t have to be.

Long after his spying days were over Berg would pass friends on the street without a tic of recognition, or at best with finger to lips in the ssshhhh mode. He hid a lot; in Rockefeller Center, behind a pillar; in a park in Bad Homburg, plainly visible behind a bush bare of leaves. In a Newark coffee shop he chanced upon Jackie Robinson, whom he had never met, whispered in his ear from behind and walked off. In Los Angeles, he had a sudden, urgent “appointment” in a restroom at City Hall. In mid-Manhattan traffic he abruptly left his taxi to board another bearing a total stranger. For these and a full quorum of quirks there was no apparent reason, no explanation. Only ssshhhh.

For his 25 postwar years Berg had no money, no assets, no job, no address (he picked up his mail at a Boston newsstand), no possessions save a succession of identical black suits and a bonanza of books stashed all over the country. What he did have, writes Dawidoff in a typically eloquent passage, “were experiences, signal moments gathered like pretty quartz stones along the shore and then fingered again and again until they were polished to a shimmer.”

In the end, Berg lived off these experiences, and off an innate allure, a man who could charm the socks off a White House cat. Chance acquaintances were happy to put him up for months. Doctors would operate gratis. Even railway conductors, no less vulnerable, would let him ride for free. He’d earned it, Dawidoff somehow implies, and somehow the reader agrees, though not quite sure why. Even in print, Berg exudes magnetism, even in “a life of abiding strangeness,” a life “resonant with ambiguity” from the first breath.

It had something to do with being Jewish, Dawidoff thinks. Like his father--who left his Ukranian village because it was “too Jewish” and opened a pharmacy in a Christian neighborhood of Newark--Berg was “drawn to patrician settings where he was the exception”: Princeton, baseball (not exactly patrician but no minyan either), the “devotedly collegial” OSS. “Branded with the mark of a faith he had been raised to resist,” Berg nevertheless prevailed on his own terms.

Described under his yearbook photo as “A Hebrew,” Berg--tall, solid, darkly handsome--became “the best baseball player in Princeton’s history,” thanks in small part to confusing the foe by exchanging infield signals in Latin. Big-league baseball was less discerning: After a frantic search for a Jewish player to boost attendance, the Giants finally signed one, whereupon vendors were ordered to hawk “ice-cream Cohens.”

Torn between the law and a game he loved almost beyond reason, Berg was advised by a friend to “take the baseball career; the law can wait.” (He had his cake and ate it: 19 years in the majors and a law degree from Columbia in his spare time.) Converted to catcher after an injury, the original “good field, no hit,” the “savant in shin guards” intrigued the press, bemused his teammates and nonplussed managers (caught reading on the bench, Berg told Red Sox manager Joe Cronin: “You lead your life and I’ll lead mine and next year we’ll beat the Yankees”).

It was a convenient arrangement: Baseball had a character and a first-rate catcher; Berg had the time and money to traipse about the globe. Then came the war.

Even pariahs are patriotic, and Berg was surely that. He also was the perfect spy. He was perfect “because he was a man who found it easy to make other people talk about themselves while keeping himself a secret, and because he was a loner with a penchant for disappearing.” He loved the spy game too--its travel, its intrigues, its exquisite silences, its exalted contacts and companions. Free-wheeling, swashbuckling OSS chief Wild Bill Donovan had found his man, and he knew what to do with him.

Bergian spy-stories are legion--mainly foreign legion: Nobody, including the OSS, was ever sure where he was. His primary assignment, though, was of vital importance to the Allies. Berg, among others, was to track and assess Nazi Germany’s progress toward manufacture of a nuclear bomb--”the greatest secret in the world.” To that end, he was to ferret out German physicists’ quondam colleagues--in Switzerland, Italy, Scandinavia--and pump them dry. More specifically, he was to locate the fabled Heisenberg, anti-Nazi but pro-Germany and “the greatest theoretical physicist in the world.” Berg not only found him, he met him, while posing (at 42) as a Swiss student. Further, an OSS team member recalls, “If anything Heisenberg said convinced him the Germans were close to a bomb, then his job was to shoot him--right there in the auditorium.”

The Germans, it turned out, were not close, a fact that shouldn’t, and didn’t, diminish Berg’s skills at espionage. Though he bumbled occasionally--he simply could not keep his .45 tucked safely in his pants--his prolific and detailed reports on Axis weaponry and technology were invaluable to America’s war effort, earning Berg a Medal of Freedom (which, true to type, he refused). Berg himself was ecstatic with his role. Then the war ended.

For most, the war had played havoc with their lives. For Berg, “returning home was the disruption.” To his chagrin, the spying was over. While the OSS “thrived on spontaneity,” its successor, the CIA, was far more structured. And structured Berg was not. His became “a life without calendar. . . . He wandered aimlessly, unburdened by appointment, salary or obligation . . . living on wit and charm and the kindness of friends.”

Concluding his graceful, fluent study, Dawidoff deplores the waste of a life but remains drawn to “a character of fantastic complication who brought pleasure and fascination to nearly everyone he brushed against.”

He died, this catcher/spy, in 1972. His burial site? Nobody knows. Berg would have loved it.