The Justice Department sought 1,745 secret wiretapping warrants in 2011, an increase of 239 over 2010, according to correspondence sent to Congressional leaders and oversight committees posted on the Justice Department website.  The secret warrants are governed under the Foreign Intelligence Surveillance Act (FISA) and are used in terrorist and espionage investigations by the FBI. The secret warrants are prepared by FBI agents and prosecutors to present to the secret Foreign Intelligence Surveillance Court in Washington.

Sent to Congressional leaders and Vice President Joseph Biden, the letter from Assistant Attorney General Ronald Weich said, "During the calendar year 2011, the government made 1,745 applications to the Foreign Intelligence Surveillance Court ( hereinafter FISC) …for authority to conduct electronic surveillance and/or physical searches for foreign intelligence purposes."

A copy of the letters can be viewed here.

The letter says that 1,676 of the applications were for electronic surveillance. It is impossible to determine based on the information made available if the 69 other warrants were for physical searches during terrorism and espionage investigations.  Some FISA warrants can cover both electronic intercepts and physical searches when FBI agents secretly enter an area and pull information off of computers or documents they are seeking as part of their investigation.

Justice Department spokesman Dean Boyd declined to comment on any specific reasons for the fluctuations in the numbers.

"The number of applications that the government submits to the Foreign Intelligence Surveillance Court (FISC) to conduct court-authorized surveillance in national security matters varies from year-to-year and depends on myriad of different factors.  The annual numbers have gone up and down and up over the past decade."  Boyd said when asked about the change in numbers.

The number of FISA applications was highest in 2007 when there were 2,370 applications to conduct electronic and physical surveillance. The number steadily grew after the 9/11 attacks.

Changes to the law in 2008 by Congress changed parts of the law, and the numbers dropped significantly.  Before the changes were enacted a FISA warrant was needed to conduct surveillance on two foreign targets overseas if the surveillance was conducted for communications that passed on any U.S.-based circuits such as emails or Internet phones that may be routed through U.S. computer servers.

The Bush administration had established the controversial Terrorist Surveillance Program which allowed the NSA to wiretap terrorism suspects inside the United States if they were contacting known al Qaeda suspects overseas without a FISA warrant. The program known as Stellar Wind was eventually canceled and brought under review by the FISC.

The new Justice Department letter dated April 30, 2012 also notes that the FBI issued 16,511 National Security Letters (NSL) to obtain certain records and information in investigations. The letter asserts that the requests were for investigations relating to 7,201 different US persons. The number of National Security Letters declined dramatically from 2010 when the FBI had sought 24,287 NSLs.

In the immediate years after the 9/11 attacks the Justice Department Inspector General found that NSLs were overused by FBI agents to gather information.

The FBI submitted 205 requests to the Foreign Intelligence Surveillance Court under Section 215 of the USA PATRIOT Act, the so-called "Library Provision," which allows the FBI to obtain business record information. This number almost doubled when compared to the 2010 numbers when 96 section 215 orders were submitted to the court.

Certain sections of the Foreign Intelligence Surveillance Act are slated to expire at the end of 2012. Attorney General Eric Holder and Director of National Intelligence James Clapper sent a letter in February to Congressional leaders urging them to reauthorize the sections of the law that are set to expire.

A background policy paper prepared by the Justice Department and the Director of National Intelligence said, "It is essential that these authorities remain in place without interruption - and without threat of interruption - so that those who have been entrusted with their use can continue to protect the nation from its enemies."