If history is any indication, the identity of the administration official who allegedly leaked the name of a CIA officer married to a critic of President Bush will likely remain a mystery.

Although the Justice Department receives about 50 leak referrals every year from the CIA and other government agencies, just two government employees have been convicted of providing classified information to the media in the last 50 years.

“It is relatively rare that leakers are discovered unless they are highly incautious or make a mistake, so past leak investigations have tended to embolden leakers rather than discourage them,” said Jonathan Turley, law professor at George Washington University.

President Bush has said he will make it a high priority to catch the individual who revealed the name of Valerie Plame (search), a CIA employee who is married to former Ambassador Joe Wilson (search). Wilson has accused the Bush administration of trumping up its evidence against Iraq to justify war there. He has claimed Plame's name, revealed by columnist Robert Novak (search) and two Newsday reporters, was offered as payback for his public criticisms of the administration.

While the White House is reviewing thousands of documents relating to the leak investigation that it plans to turn over to the Justice Department, Bush has conceded that an investigation may not uncover the truth.

Asked last week by a reporter how confident he is that the leaker's identity will be discovered, Bush returned volley by asking how many sources reporters have exposed. 

"Probably none," Bush said, answering his own question. "I mean, this is a town full of people who like to leak information. I have no idea whether we'll find out who the leaker is, partially because, in all due respect to your profession, you do a very good job of protecting the leakers.”

Reporters justify withholding sources' names for fear that if they do so, no contacts would ever trust them in the future. Reporters have spent time in jail and publishers have paid substantial fines to avoid releasing the names of sources. According to law, a reporter cannot be charged for revealing the classified name of an intelligence agency official.

Attorney General John Ashcroft, whose department is conducting the investigation, has previously indicated frustration with investigations of administrative leaks.

“In most cases, identifying the individual who disclosed classified information without authority has been difficult, at best," Ashcroft wrote in a letter to House Speaker Dennis Hastert, R-Ill., last year. "The seriousness of the issue has outpaced the capacity of extant administrative and law enforcement mechanisms to address the problem effectively.”

In his letter, Ashcroft said past probes have failed to deter, identify and punish leakers. He suggested that investigators will consider new approaches to uncovering individuals who reveal classified information. Individuals who leak classified information can face penalties of up to 10 years in prison and a $50,000 fine.

Despite the large number of referrals each year, only two leakers have been successfully prosecuted in the past five decades, both within the last 20 years.

In 1986, Navy intelligence analyst Samuel Morrison was sentenced to two years in prison for espionage and theft of government property relating to his 1984 handover of three spy satellite photographs to Jane’s Defence Weekly. Former Atlanta-based Drug Enforcement Administration analyst Jonathan Randel was convicted in 2003 of selling restricted federal information. He was ordered to serve one year in prison and three years supervised release.

Watergate offers a clear example of just how difficult it is to catch a White House leaker.

President Richard Nixon’s administration was scandalized by Washington Post stories that relied on an individual known as “Deep Throat,” an administration source whose identity still remains a mystery.

Nixon had been known to use FBI wiretaps to listen in on the conversations of White House staff and press, but Deep Throat's identity — whether one leaker or several — is one of Washington's best-kept secrets. Former Washington Post reporters Bob Woodward (search) and Carl Bernstein (search), who featured Deep Throat in their investigative stories on the White House's financing of intelligence gathering activities against the Democrats, have said they would reveal Deep Throat's identity only after his death.

Leaks are extremely common in Washington, but are rarely as serious as the current one under investigation.

Often, leaks are used as trial balloons to gauge support for programs from which the administration may later distance itself. Leaks are also used to demonstrate military successes, for instance, revealing the details of a bombing raid, which usually involves unleashing classified information.

“Leaks are the coin of the realm in this city. It’s a communication system between journalists and government officials that relies importantly on leaks as a way of communicating with the people,” said Stephen Hess, who served in the Eisenhower and Nixon administrations and is now a fellow at the Brookings Institution (search).

Despite the poor record of uncovering leaks, some aspects of the current case give hope that the leaker will be uncovered.

“The difference between this case and many others is the leaking of a name of a CIA agent does have the potential to endanger lives,” Hess said. As a result of the seriousness of this case, “the administration could be more active and aggressive in pursuing the leaker.”

Turley also gave this case a higher likelihood of success.

“What’s different is that whoever leaked this information does not appear to be particularly good at it. Whoever did it violated a number of standard operating procedures for leaks,” he said.

Turley said in general, leakers contact one reporter with whom they have a relationship. In this case, the leaker is said to have contacted as many as six reporters, and as a result, more phone records are available for examination and more individuals have first-hand knowledge of the leak.

Turley questioned whether the leaker might be new to Washington and have made a rookie mistake.

Still, catching the leaker could be difficult because the reporter who reveals his source could effectively end his career.

“Usually I bet against catching leakers. On this one, I would give even money,” Turley said.