President Bush signed a directive this month that expands the intelligence community's role in monitoring Internet traffic to protect against a rising number of attacks on federal agencies' computer systems. The directive, whose content is classified, authorizes the intelligence agencies, in particular the National Security Agency, to monitor the computer networks of all federal agencies -- including ones they have not previously monitored. The NSA has particular expertise in monitoring a vast, complex array of communications systems -- traditionally overseas. The prospect of aiming that power at domestic networks is raising concerns, just as the NSA's role in the government's warrantless domestic-surveillance program has been controversial. Agencies designed to gather intelligence on foreign entities should not be in charge of monitoring our computer systems here at home," said Rep. Bennie Thompson (D-Miss.), chairman of the House Homeland Security Committee. The classified joint directive, signed Jan. 8 and called the National Security Presidential Directive 54/Homeland Security Presidential Directive 23, has not been previously disclosed. Allowing a spy agency to monitor domestic networks is worrisome, said James X. Dempsey, policy director of the Center for Democracy and Technology. "We're concerned that the NSA is claiming such a large role over the security of unclassified systems," he said. "They are a spy agency as well as a communications security agency. They operate in total secrecy. That's not necessary and not the most effective way to protect unclassified systems."