ETERSON AIR FORCE BASE, Colo. ó At about 8:45 most mornings, in a conference room at this base at the foot of the Rocky Mountains, representatives of the Central Intelligence Agency, Federal Bureau of Investigation and a dozen other federal agencies meet to debate how the Pentagon should respond if terrorists strike again in the United States.

The meeting's host, Gen. Ralph E. Eberhart of the Air Force, a four-star general who is now the nation's top officer responsible for domestic security, mulls over doomsday scenarios for a new wave of attacks by Al Qaeda or some other terrorist group.

"By air or ship or truck or suicide bomber," General Eberhart said in a recent interview, listing the threats that he must be ready to confront as the head of the military's new Northern Command. "Medical scenarios: smallpox, you name the disease that we might be involved in in terms of quarantine."

"What if an airport is attacked, or a seaport?" he continued. "You name the infrastructure. It could be a bridge, it could be an oil refinery, the list goes on and on. We can all envision the terrible things that might happen."

For up to an hour each day in what is blandly called "the commander's situational awareness meeting," General Eberhart asks representatives of each of the 14 agencies ó a roster that also includes the State Department, the National Security Agency, NASA and the Federal Aviation Administration ó for updates from their experts, and advice on what he should do if the worst happens.

"What we're trying to prepare ourselves for is the God-awful possibility that there could be two or three at the same time, and they could be different in nature," General Eberhart said.

For now, officials say, the daily discussion is speculative: imagining and preparing for whatever terrorists might unleash within American borders.

But there is every expectation back in Washington and certainly here, in the headquarters of the Northern Command, that if terrorists strike again inside the United States, General Eberhart and his deputies will find themselves directing a large part of the federal government's response.

In a large-scale terrorist attack, especially if there is any threat of the use of chemical, biological or nuclear weapons that could overwhelm the ability of state and local governments to respond, the Northern Command would probably take charge of the scene, directing the response from a command post bored deep in a mountain a few miles from this installation in Colorado Springs.

"I guess you could conjure up a situation where it was so bad that no one else had the capability to be in charge," General Eberhart said. "We could be in charge at that point."

His emergency command center, part of a 4.5-acre bunker complex buried 2,000 feet into Cheyenne Mountain, was built in the 1960's to enable the United States to detect and respond to a nuclear attack from the Soviet Union.

Today, video screens in the command center that once monitored activity in Russian missile silos and the location of Soviet bombers instead display the air-traffic control network for thousands of civilian planes flying over the continental United States.

A legacy of the Sept. 11 terror attacks, the Northern Command began operations in October to coordinate the military's response to threats against the United States and its territorial waters.

While it has few troops under its direct control, the command now has a staff of about 500 people, both military and civilian, and can draw on tens of thousands of troops in a matter of hours if there is a domestic emergency demanding the Pentagon's response.

The Northern Command coordinated the deployment of Army RC-7 airborne reconnaissance low-surveillance planes to the Washington area during the sniper attacks this fall. It dispatched maritime forces off the coast of Cabo San Lucas, Mexico, where President Bush attended the Asia Pacific Economic Cooperation summit in October.

The command is operating on a budget of $81 million this fiscal year, which is expected to grow by about $20 million a year through 2008.

The staff includes full-time representatives of civilian agencies like the F.B.I., the C.I.A. and the State Department, that otherwise rarely answer directly to the Pentagon.

The F.B.I. representative is a former Air Force officer with a background in countering domestic terrorism; the C.I.A. representative is a former undercover officer who has held assignments for the agency in Asia and Central America; and the State Department adviser is a career Foreign Service officer who was recently posted in Afghanistan. (All agreed to be interviewed on condition they not be named.)

The close ties that are being established here between the Defense Department and federal law enforcement and intelligence agencies have already given pause to civil liberties groups that the military will be given too much authority to intrude in the lives of American civilians as it fights terrorism.

Among those advising General Eberhart is Col. Jarisse J. Sanborn, the senior legal adviser, who is asked to weigh whether the command's proposed duties might interfere with federal laws that restrict the domestic role of the military. In particular, the Posse Comitatus Act of 1878 bars troops from direct involvement in domestic law enforcement duties, like arrests and detentions.

"Everything we do has to be looked at," Colonel Sanborn said.

General Eberhart, a decorated combat pilot, says that he is sensitive to the concerns of civil libertarians and that he would respond to a terrorist attack only at the express direction of the White House and the Pentagon, and at the request of local authorities.

"We also understand Civics 101," he said. "I really don't think, based on those checks and balances, that we're going to get into a situation where the military will be doing things that should be done by other agencies, either in the federal government or by state and local governments."