The mystery within the mystery concerning Robert Hanssen, accused of spying for the Soviet Union for more than 15 years, is simply what motivated him to do it? With no signs of pro-Soviet ideological commitment or extravagant spending, the answer may lie in Hanssen's membership in Opus Dei, an ultraconservative Catholic organization. PNS commentator Yoichi Clark Shimatsu is former editor of The Japan Times Weekly in Tokyo, and has reported on the Aum Shinrikyo sect.

Intelligence experts and congressional committees are puzzling over what motivated FBI agent Robert Hanssen to spy for Moscow over the past 15 years.

Money seems to offer no clues, because Hanssen lived in an ascetic style. Nor is there yet any evidence that this happily married man fell into a "honey trap" involving a coy Natasha.

The search for a motive is complicated by the fact that his colleagues say that Hanssen was fiercely anticommunist and a devout member of Opus Dei, an ultraconservative Catholic organization. He was a regular parishioner of St. Catherine of Siena Church, in a Virginia suburb of the capital, where an elite congregation, which includes Supreme Court justice Antonia Scalia, attend traditional Latin masses.

It might be reassuring to believe that Hanssen acted alone. But if that is the case, he would likely have repented and confessed all. The opposite reaction -- his stony silence -- indicates something other than the sins of a prodigal son.

Hanssen's one-word explanation for his treason, according to an FBI affidavit, was "loyalty." It may well be that his loyalty -- to Opus Dei and, by extension, the foreign service of the Vatican state -- hold the key to the mystery.

Opus Dei, Latin for "Work of God," is a secretive lay group within the body of the Catholic Church, with more than 80,000 members worldwide. As the only personal prelature in the Church, it is an entity unto itself, separate from the diocesan structure.

Founded in the late 1920s by Spanish priest Josemaria Escriva, Opus Dei assumed a political role from the start, openly siding with the Franco dictatorship. Its members served in cabinets while Spain was allied with Hitler and Mussolini.

Opus Dei floundered in the wake of World War II, but regained impetus under Pope John Paul II, after providing crucial support for his papal candidacy. In the Polish pope, the group found a champion willing to back its harsh stance against abortion, birth control, its crusade against communism, the push for Catholicism as a state religion, and war on left-leaning liberation theologians within the church.

It may seem paradoxical that Hanssen would spy for the Soviet Union, a moral adversary and indeed a satanic force in the eyes of Opus Dei. During Gorbachev's glasnost era, however, there is evidence of behind-the-scenes collaboration between the Vatican and Moscow. In particular, Vatican Secretary of State Cardinal Agostino Casaroli, a powerful Opus Dei supporter, pursued a policy of reaching out toward Moscow with the aim of gaining Poland's release from the Warsaw Pact.

Rivers of money, much of it provided by Bill Casey's CIA, poured into Warsaw and Moscow, and the Vatican found ready support from the U.S. because the security establishment under President Ronald Reagan was packed with conservative Catholics, including Casey, Richard Allen and William Clark.

Hanssen's most damaging activities in FBI counterintelligence coincided with these years, 1985-89. Secrets from America's intelligence vaults could well have been part of the quid pro quo in the late cardinal's dance with Moscow.

Certainly, the Vatican has had no qualms about violating American sensitivities. Indeed, it seems to reflect a Eurocentric triumphalism. The papal encyclical on labor rights slapped rampant materialism -- that is, the immoral United States -- as the "other" great evil afoot in the world.

The Vatican's political work with Moscow paid off handsomely with the independence of Catholic-dominant Hungary, Czechoslovakia, Ukraine and later, from Moscow's nominal ally Yugoslavia, of Slovenia and Croatia. All the while, Hanssen kept up the flow of U.S. secrets to Moscow.

Why might a conscientious Catholic be accused of betraying the FBI's Russian recruits to the firing squad? Hanssen has spoken of his schoolboy fascination with a book about Kim Philby, Britain's notorious turncoat spy (a claim flawed by the fact that "The Philby Conspiracy" was published after Hanssen graduated from high school).

But Hanssen may well have read John LeCarre's 1974 "Tinker, Tailor, Soldier, Spy," based on the Philby saga, in which a high-ranking mole betrays his fellow agents in order to advance his career inside the British intelligence bureaucracy. As Moscow rolls up their spy rings, his rivals, one by one, lose their chances for promotion, while the double agent becomes the golden boy headed for the pinnacle of power.

The plot of "Tinker, Tailor" bears a disturbing resemblance to the recent chaos inside U.S. intelligence. Did Hanssen clear the path to the FBI directorate for his fellow Opus Dei member Louis Freeh? This possibility cannot be dismissed, nor should reluctance to interfere with a religious organization prevent a probe into Hanssen's ties within Opus Dei.

In nearly every case involving a secretive sect, like the Branch Davidians or Aum Shinrikyo, law enforcement authorities have erred on the side of acting too slowly.

For the faithful, the response to the Hanssen affair should not be limited to sermons about a lost sheep tangled in Satan's snares. Opus Dei, models itself after the Counter-Reformation, appears to be repeating the worst mistakes from that chapter of church history. As the church became engrossed in the fates of nations, its moral certitude against Protestant dissent was lost. The institutional paranoia of the Inquisition gave rise to the secret police of Cardinal Richelieu who were at the service of the state.