SOUTH POMFRET, Vt. — Preoccupied with the war in Iraq and still traumatized by Sept. 11, 2001, the American public has paid little attention to some of what is being done inside the United States in the name of anti-terrorism. Under the banner of "homeland security," the military and intelligence communities are implementing far-reaching changes that blur the lines between terrorism and other kinds of crises and will break down long-established barriers to military action and surveillance within the U.S.

"We must start thinking differently," says Air Force Gen. Ralph E. "Ed" Eberhart, the newly installed commander of Northern Command, the military's homeland security arm. Before 9/11, he says, the military and intelligence systems were focused on "the away game" and not properly focused on "the home game." "Home," of course, is the United States.

Eberhart's Colorado-based command is charged with enhancing homeland security in two ways: by improving the military's capability to defend the country's borders, coasts and airspace — unquestionably within the military's long-established mission — and by providing "military assistance to civil authorities" when authorized by the secretary of Defense or the president.

That too may sound unexceptionable: The military has long had mechanisms to respond to a request for help from state governors. New after 9/11 are more aggressive preparations and the presumption that local government will not be able to carry the new homeland security load. Being the military, moreover, contingency planners approach preparing by assuming the worst. All of this is a major — and potentially dangerous — departure from past policy.

The U.S. military operates under the 1878 Posse Comitatus Act, which prohibits the direct use of federal troops "to execute the laws" of the United States. The courts have interpreted this to mean that the military is prohibited from any active role in direct civilian law enforcement, such as search, seizure or arrest of civilians.

"There are abundant reasons for rejecting the further expansion of the military's domestic role," says Mackubin T. Owens, a professor of strategy and force planning at the Naval War College. Looking at the issue historically, Owens wrote in an August 2002 essay in the National Review's online edition that "the use of soldiers as a posse [places] them in the uncomfortable position of taking orders from local authorities who had an interest in the disputes that provoked the unrest in the first place." Moreover, Owens said, becoming more involved in domestic policing can be "subtle and subversive … like a lymphoma or termite infestation." Though we are far from having "tanks rumbling through the streets," he said, the potential long-term effect of an increasing military role in police and law enforcement activities is "a military contemptuous of American society and unresponsive to civilian authorities."

Eberhart says his Northern Command operates scrupulously within the bounds of the law. "We believe the [Posse Comitatus] Act, as amended, provides the authority we need to do our job, and no modification is needed at this time," he told the House Armed Services Committee in March.

Of course, what he knows is that amendments approved by Congress in 1996 for that earlier civilian war, the war on drugs, have already expanded the military's domestic powers so that Washington can act unilaterally in dispatching the military without waiting for a state's request for help. Long before 9/11, Congress authorized the military to assist local law enforcement officials in domestic "drug interdiction" and during terrorist incidents involving weapons of mass destruction. Furthermore, the president, after proclaiming a state of emergency, can authorize additional actions.

Indeed, the military is presently operating under just such an emergency declaration. Eberhart's command has defined three levels of operations, each of which triggers a larger set of authorized activities. The levels are "extraordinary," "emergency" and "temporary." At the "temporary" level, which covers such things as the Olympic Games or the Super Bowl, limited assistance can be provided to law enforcement agencies when a governor requests it, primarily in such areas as logistics, transportation and communications. During "emergencies," the military can provide similar support, mostly in response to specific events such as the attacks on the World Trade Center.

It is only in the case of "extraordinary" domestic operations that the unique capabilities of the Defense Department are deployed. These include not just such things as air patrols to shoot down hijacked planes or the defusing of bombs and other explosives, , but also bringing in intelligence collectors, special operators and even full combat troops.

Given the absence of terrorist attacks inside the United States since 9/11, it may seem surprising that Northern Command is already working under the far-reaching authority that goes with "extraordinary operations." But it is.

"We are not going to be out there spying on people," Eberhart told PBS' NewsHour in September. But, he said, "We get information from people who do." Some of that information increasingly comes not from the FBI or those charged with civilian law enforcement but from a Pentagon organization established last year, the Counterintelligence Field Activity (CIFA). The seemingly innocuous CIFA was originally given the mission of protecting the Defense Department and its personnel, as well as "critical infrastructure," against espionage conducted by terrorists and foreign intelligence services.

But in August, Defense Secretary Donald H. Rumsfeld expanded CIFA's mission, charging it with maintaining "a domestic law enforcement database that includes information related to potential terrorist threats directed against the Department of Defense." The group's Assessments and Technology Directorate, which shares offices with the Justice Department's Foreign Terrorist Tracking Task Force, has already identified 200 foreign terrorist suspects in the U.S., according to a Defense Department report to Congress.

This year, the Pentagon inspector general authorized assigning military special agents to 56 FBI Joint Terrorism Task Force operations at FBI field offices. These military agents will pursue leads in local communities of potential threats to the military. Eberhart also plans to have his own cadre of agents working with local law enforcement. Next year, he plans to transform Joint Task Force Six, a drug interdiction unit of 160 military personnel at Ft. Bliss, Texas, into Joint Interagency Task Force North. The new task force will be given nationwide responsibility for working with law enforcement agencies.

CIFA, moreover, has been given a domestic "data mining" mission: figuring out a way to process massive sets of public records, intercepted communications, credit card accounts, etc., to find "actionable intelligence." "Homeland defense relies on the sharing of actionable intelligence among the appropriate federal, state, and local agencies," says Lt. Gen. Edward G. Anderson III, Eberhart's deputy.

Another ambitious domestic project is being undertaken by the National Geospatial-Intelligence Agency, which is gathering "geospatial information" about 133 cities, the borders and seaports. This "urban data inventory" combines unclassified and classified data (including such things as the location of emergency services, communications, transportation and food supplies) with a high-resolution satellite map of the United States. When the mapping efforts are completed, a national "spatial data infrastructure" will be created down to the house level. Intelligence analysts speak of one day being able to identify individual occupants, as well as their national background and political affiliations. Though the military is just getting its systems in place, there can be no other conclusion: Domestic surveillance is back.

It's not that we're heading toward martial law. We're not. But outside the view of most of the public, the government is daily expanding military operations into areas of local government and law enforcement that historically have been off-limits. And it doesn't seem far-fetched to imagine that those charged with assembling "actionable intelligence" will slowly start combining databases of known terrorists with seemingly innocuous lists of contributors to charities or causes, that membership lists for activist organizations will be folded in, that names and personal data of anti-globalization protesters will be run through the "data mine." After all, the mission of Northern Command and other Pentagon agencies is to identify groups and individuals who could potentially pose threats to Defense Department and civilian installations.

Given all this, it might be a good time for state and local governments to ask themselves whether the federal government, through the military, is slowly eroding their power to manage what — for very good reasons — have always been considered local responsibilities.