While President Obama and his intelligence advisers have spoken of the surveillance programs leaked by Mr. Snowden mainly in terms of combating terrorism, the court has also interpreted the law in ways that extend into other national security concerns. In one recent case, for instance, intelligence officials were able to get access to an e-mail attachment sent within the United States because they said they were worried that the e-mail contained a schematic drawing or a diagram possibly connected to Iran’s nuclear program.

In the past, that probably would have required a court warrant because the suspicious e-mail involved American communications. In this case, however, a little-noticed provision in a 2008 law, expanding the definition of “foreign intelligence” to include “weapons of mass destruction,” was used to justify access to the message.

The court’s use of that language has allowed intelligence officials to get wider access to data and communications that they believe may be linked to nuclear proliferation, the officials said. They added that other secret findings had eased access to data on espionage, cyberattacks and other possible threats connected to foreign intelligence.

“The definition of ‘foreign intelligence’ is very broad,” another former intelligence official said in an interview. “An espionage target, a nuclear proliferation target, that all falls within FISA, and the court has signed off on that.”