Ms Linda Tripp finished her eight days of testimony before the grand jury investigating the Monica Lewinsky affair, saying that she learned of "dangerous information" while working at the White House.
Ms Tripp's revelation last January that she taped 20 hours of conversations with the former White House intern led to the investigation.
Breaking her seven-month silence in an emotional statement to the media outside the federal courthouse in Washington, Ms Tripp said she went to the independent counsel, Mr Kenneth Starr, out of fear.
"I became aware between 1993 and 1997 of actions by high government officials that may have been against the law," Ms Tripp said. She became "increasingly fearful that this information was dangerous, very dangerous to possess".
Flanked by her grown-up son and daughter, Ms Tripp also complained bitterly at the way supporters of President Clinton had vilified her and how late-night comedians cruelly mocked and mimicked her. She asked people to imagine the pain of her children as they heard "an endless barrage of lies" about her.
Saying she had testified "truthfully and completely" to the grand jury in a record number of appearances, Ms Tripp said she hoped all remaining witnesses would do the same, in an apparent reference to Ms Lewinsky and President Clinton.
Ms Tripp also took strong issue with statements attributed to Ms Lewinsky that she (Ms Tripp) helped in the drawing up of the "so-called talking points". This was a document which Ms Tripp was given by Ms Lewinsky to help her avoid telling the full truth in the Paula Jones action against President Clinton for sexual harassment. Ms Tripp said that allegations that she contributed to the talking points were "patently false".
She said that "fear was no longer to be my master" when she approached Mr Starr on January 12th to tell him about her taped conversations with Ms Lewinsky, in which she spoke at length about an alleged affair with President Clinton while she was a White House intern and later working at the Pentagon.
Saying she was an average American, she said she wanted people to know who she was and how she came to be the central figure in the case.
"I am you, I am just like you," she said, standing outside the courthouse where the grand jury meets. "I am an average American who found herself in a situation not of her own making.
"I have been vilified for having taken the path of truth. I have been maligned by people who have chosen not to tell the truth and who know they are not telling the truth. That is a pretty frightening thing."
Ms Tripp, who worked at the White House before transferring to the Pentagon, worked with Ms Lewinsky in both places.
Ms Tripp's statement came after Mr Clinton's lawyer, Mr David Kendall, negotiated a deal to save him being the first sitting President to testify in person before a grand jury under subpoena. His lawyer had sought a forum for Mr Clinton to give his testimony outside a courthouse.
As part of the agreement, Mr Starr withdrew the historic subpoena, said a senior White House official. Mr Kendall went to the White House to brief Mr Clinton just after reaching the agreement with Mr Starr yesterday afternoon.
By testifying on August 17th, Mr Clinton would be delaying by two days his summer vacation with his wife Hillary and daughter Chelsea.