Washington ? Maybe it was just curiosity.

But whatever led State Department workers to pry into the passport files of Hillary Rodham Clinton, Barack Obama and John McCain, it wasn’t an accident.

Each time agency workers go into someone’s electronic personal files, the system reminds them that such information is restricted under privacy laws and may be reviewed only on a need-to-know basis. It also reminds them that penalties will be imposed if the information is being improperly checked.

The warning wasn’t enough for at least four department workers who were caught prying into the presidential candidates’ files, an embarrassing episode that led Secretary of State Condoleezza Rice to telephone the candidates with her personal apology Friday and to promise a full investigation.

The snooping incidents raised questions as to whether there was political motivation and why two contractors involved were fired before investigators had a chance to interview them. The State Department’s inspector general was probing, with the Justice Department monitoring the effort, but Obama said that was not enough. He urged congressional involvement “so it’s not simply an internal matter.”

The unauthorized digging into electronic government files on politicians recalled a 1992 case in which a Republican political appointee at the State Department was demoted for searching Bill Clinton’s passport records when Clinton was running against President George H.W. Bush.

McCain, the Republican nominee-in-waiting, said there should be an investigation of the new snooping as well as an apology.

Democrat Obama said that better include Congress, not just Bush administration investigators.

“When you have not just one but a series of attempts to tap into people’s personal records, that’s a problem not just for me but for how our government functions,” Obama told reporters in Portland, Ore., where he was campaigning. “I expect a full and thorough investigation. It should be done in conjunction with those congressional committees that have oversight function so it’s not simply an internal matter.”

Rice was apologetic in public as well as in her private phone calls to the candidates.

“None of us wants to have a circumstance in which any American’s passport file is looked at in an unauthorized way,” the secretary of state said after speaking with Obama.

“I told him that I was sorry, and I told him that I, myself, would be very disturbed if I learned that somebody had looked into my passport file,” she added. “And therefore, I will stay on top of it and get to the bottom of it.”

In all, at least four workers were involved in the snooping.