s most embarrassing counterintelligence failures in recent years. The bureau is the principal federal agency responsible for ferreting out spies against the United States. Over the years, Mr. Hanssen received several promotions, rising through the F.B.I.'s counterintelligence ranks even while, officials said, he was secretly supplying the Russians with highly classified data after 1991 when the Soviet empire collapsed. "The trusted insider betrayed his trust without detection," Mr. Freeh said. Plato Cacheris, Mr. Hanssen's lawyer, said that as of now his client would plead not guilty to the charges, but added that the case was still in its early stages. Mr. Cacheris suggested that the government's case might not seem as solid as it appeared, saying that prosecutors "always talk like they have a great case, but we'll see." An F.B.I. affidavit filed in support of the charges against Mr. Hanssen, which was unsealed today, said he began his espionage in 1985 and spied undeterred for the Soviet Union and, after its collapse, for Russia. It said he continued apparently unfazed by the many changes Mr. Freeh imposed to strengthen counterespionage efforts in the aftermath of the case against Aldrich H. Ames, the C.I.A. officer sentenced to life in prison in 1994 as a spy for Moscow. The affidavit, nearly 100 pages long, provided an unusually detailed narrative account. It included details intended to support the bureau's view that Mr. Hanssen had a long career as a Soviet spy, listing the dates that officials said he had contacts with the Russians, the texts of letters officials said he wrote to Russian officials, the payments officials said he received and the nature of the material he provided Moscow. Law enforcement officials said the F.B.I. had secretly obtained the bulk of Mr. Hanssen's espionage file from the Russian intelligence service, which they said was in itself a counterintelligence coup for the United States. Mr. Freeh said Mr. Han...
