A July 2005 audit by the Justice Department's inspector general found that the bureau's counterterrorism audio backlog had doubled over the preceding year to 8,354 hours. But in their Senate report, FBI officials counter that the backlog represents only 1.35 percent of all the audio collected, and that nearly all of the agency's text and electronic data files have now been translated.

"We've made great strides," says Jeff Lanza, an FBI spokesman. "Ninety-nine percent of the backlog has been eliminated." Nearly a third of what remains is "white noise" not expected to yield anything of value, officials say. Of most concern are 3,240 hours of "audio from very obscure languages and dialects," which the bureau is scrambling to find linguists for.

The FBI has eased its backlog by markedly increasing its reservoir of translators. Since 2001, the number of FBI staff linguists has grown to 1,409, an 80 percent jump, officials say. The FBI has also turned to "the language programs of allied intelligence agencies," as well as to contract linguists, according to testimony by FBI Director Robert Mueller.

Since the 9/11 attacks in 2001, the number of national security wiretaps approved by the secret U.S. Foreign Intelligence Surveillance Court more than doubled, according to the Justice Department, from 934 in 2001 to 2,072 in 2005–an increase of 122 percent. These include wiretaps of counterterrorism suspects as well as counterintelligence targets such as foreign spies in America. In addition, thousands of electronic intercepts are thought to have been made under the National Security Agency's controversial warrantless surveillance program begun after 9/11. (That program was recently brought under the Foreign Intelligence Surveillance Court's purview.)

By contrast, the growth has been much slower in criminal wiretaps, which include eavesdropping on Mafia bosses, corrupt officials, and other suspected lawbreakers. In 2001, authorities completed 1,491 of these intercepts authorized by federal and state courts, according to the Administrative Office of the United States Courts. That number grew to 1,773 in 2005, representing an increase of 19 percent.