It's hard to imagine that poking by the State Department, under a second President Bush, into the passport files of presidential candidates is an innocent mistake.

Last week Americans learned that the Department of State had 'fessed up to employees' delving on three occasions into the passport files of Sen. Hillary Clinton, Sen. John McCain and Sen. Barack Obama. The nation was told that the look at the files had been carried out without authorization by two contract employees, who have since been fired, and a trainee, who has been reprimanded.

Secretary of State Condoleezza Rice said that she had informed all three candidates and apologized, and that an investigation of the matter would be carried out. Administration officials tried to provide assurances that the snooping cases had not been political dirty tricks -- a quest for damaging information on the three candidates -- but rather acts of idle curiosity on the part of the three employees involved.

Although it was difficult to imagine that the three weren't looking for prurient information on the candidates, the fact that the same thing happened in 1992 under the State Department of former President George H. W. Bush makes it harder to believe. Political appointees in the elder Bush's State Department were looking for dirt on his opponent at the time, Bill Clinton.

The very effort to do so was a smear in itself. There was speculation at the time that Bush I people were looking for evidence that young Bill Clinton, a Vietnam war opponent, had tried to renounce his U.S. citizenship at the American Embassy in London or Moscow.

It is hard to imagine what the Bush II employees were seeking. It is possible, of course, that they were looking for something to peddle to a campaign or the media.

At the same time, it is utterly inappropriate and a violation of the privacy of the three candidates that government employees were poking into their passport files. Sen. Arlen Specter, the Republican from Pennsylvania, has joined with other representatives in calling for a congressional -- as opposed to merely a State Department -- investigation into the matter.

We strongly support carrying out such an inquiry, on an urgent basis since the political campaign is still in full sway.