“The D.H.S. continues to monitor the Internet for criticism of the government,” she said. “This suspicionless, overbroad monitoring quells legitimate First Amendment activity and exceeds the agency’s legal authority."

A federal statute cited by officials last week as the legal basis for the program gives the National Operations Center the authority “to provide situational awareness” for officials “in the event of a natural disaster, act of terrorism or other man-made disaster” and to “ensure that critical terrorism and disaster-related information reaches government decision makers.”

Officials have stressed that the program does not collect personally identifying information, like the names or Twitter account handles of the people making comments, and that it does not monitor, review or collect First Amendment-protected speech.

Still, the program also monitors articles and broadcasts by traditional media outlets. The 2011 manual says that analysts, in addition to flagging information related to matters like terrorism and natural disasters, should also identify “media reports that reflect adversely on D.H.S. and response activities” and collect “both positive and negative reports” on department components as well organizations outside of the department.

The manual includes keywords that analysts should search for. A list of agencies in the keyword section includes not only those in the department dealing with matters like immigration and emergency management, but also the Central Intelligence Agency, several law enforcement agencies in the Justice Department, the Red Cross and the United Nations.

At the hearing last week, lawmakers of both parties said it made sense for the department to use the Internet to gather information about emerging events, but they voiced concerns that if it went further than that, the program might chill people’s freedom of speech and willingness to express dissent online.

“Other private individuals reading your Facebook status updates is different than the Department of Homeland Security reading them, analyzing them and possibly disseminating and collecting them for future purposes,” said the chairman of the subcommittee, Representative Patrick Meehan of Pennsylvania.