Publicly, the debate over the law known as the USA Patriot Act has focused on concerns from civil rights advocates that the F.B.I. has gained too much power to use expanded investigative tools to go on what could amount to fishing expeditions.
  But [newly obtained internal FBI documents] . . . offer a competing view, showing that, privately, some F.B.I. agents have felt hamstrung by their inability to get approval for using new powers under the Patriot Act, which was passed weeks after the terrorist attacks of Sept. 11, 2001.
  One internal F.B.I. message, sent in October 2003, criticized the Office of Intelligence Policy and Review at the Justice Department, which reviews and approves terrorist warrants, as regularly blocking requests from the F.B.I. to use a section of the antiterrorism law that gave the bureau broader authority to demand records from institutions like banks, Internet providers and libraries.
  "While radical militant librarians kick us around, true terrorists benefit from OIPR's failure to let us use the tools given to us," read the e-mail message, which was sent by an unidentified F.B.I. official. "This should be an OIPR priority!!!"