ssen's arrest was unrelated to the defection last October of Sergei Tretyakov, a Russian diplomat at the United Nations. Later, law enforcement officials said it was not Mr. Tretyakov who cast suspicion on Mr. Hanssen. Today, Mr. Freeh would not discuss how the F.B.I. learned of Mr. Hanssen's activities or why they had not been discovered sooner. He also would not say whether Mr. Hanssen had ever been subject to screening procedures like polygraph examination. Lie-detector tests are routinely given to F.B.I. employees who handle highly sensitive information and are authorized to deal with other countries or intelligence agencies. Mr. Freeh said Mr. Hanssen's activity "represents the most traitorous actions imaginable." He said the F.B.I. had not yet determined the full extent of the damage because agents did not want to risk tipping their hand by beginning such a review while the investigation was under way. Even so, Mr. Freeh said of the suspected damage, "We believe it was exceptionally grave." It was evident today that F.B.I. officials were bracing for what they expect to be stinging criticism in the days ahead. Mr. Freeh said his agency had agreed to the appointment of a high-level panel that will assess the extent of the damage and review security procedures at the F.B.I. The panel will be led by William H. Webster, a former director of central intelligence and the Federal Bureau of Investigation. As a reflection of the seriousness of the case, President Bush read a statement to reporters traveling with him on Air Force One, saying, "This has been a difficult day for those who love our country, especially for those who serve our country in law enforcement and intelligence." He added, "To anyone who would betray its trust, I warn you, we'll find you and we'll bring you to justice." Attorney General John Ashcroft issued a statement that said in part, "Individuals who commit treasonous acts against the United States will be held fully...
