WASHINGTON » Three times this year, the Joint Chiefs of Staff and the regional war-fighting commanders have assembled at a military base south of the capital, where a giant map of the world, larger than a basketball court, was laid out on the ground, giving the sessions an appearance of a lethally earnest game of Risk.

The generals and admirals walked the world and worked their way through a series of potential national security crises, locked in debate over what kind of military — its size, its capability — the nation will require in the next five years.

“Strategic seminar” is the name Gen. Martin E. Dempsey, chairman of the Joint Chiefs of Staff, has chosen for these daylong sessions, which were not exactly a war game more than a tabletop military exercise, and unlike anything the Pentagon has done to plan its future.

Shortly after being sworn in as chairman in October, a decade after the terrorist attacks of Sept. 11, 2001, Dempsey said the military was confronting “a strategic inflection point, where the institution fundamentally re-examines itself.” The seminar project he started fits his goal: to try to build the right military force for five years from now — and not be driven by the budget cycle into a series of year-by-year decisions.

The overarching question is whether the Pentagon’s war plans need to be rewritten to take into account how the military has been affected by a decade of fighting in Iraq and Afghanistan, and now by orders to shrink to fit mandated budget cuts. While the list of potential adversaries and the rising threats remain classified, the assessments from the sessions already are reshaping military planning. Initial findings have been presented to President Barack Obama by Dempsey, officials said.

One realization is that under any situation in which the United States is in an armed conflict within five years, U.S. territory most likely would be attacked as part of an adversary’s actions, regardless of where the major fighting was focused overseas. That attack might be direct, by missile, or more asymmetrical, as in terrorism or via a computer-network cyberattack.

“In the future, our homeland will not be the sanctuary it has been,” Dempsey told a recent military conference, during which he pulled back the curtain — a bit — on the strategic seminar project.

As a result of that seminar, Dempsey said, the military’s Northern Command, responsible for defending U.S. territory, has begun work with the Department of Homeland Security, the FBI and other domestic agencies to assess how potential demands for military forces overseas might affect security at home, and how any shortfalls could be resolved.

Another lesson from the seminars is that the Pentagon might have to organize and deploy forces in a different way than war plans now dictate if there is another major conflict overseas and simultaneously a significant attack at home, or the need to manage a catastrophic, domestic natural disaster.

“We assumed a conflict someplace, and we flowed the forces required to that conflict,” Dempsey said. “We created a scenario where the homeland was attacked — or even if it wasn’t attacked, where there might have been some natural disaster. And it was remarkable.”

Dempsey acknowledged that the Pentagon had long believed “there’s always enough at home to deal with whatever happens, even while we’re fighting conflict elsewhere,” especially if the National Guard or reserves were used. After the seminar, he noted, “We might have to challenge that assumption.”

Gen. Ray Odierno, the Army chief of staff, told a public forum sponsored by the magazine Foreign Affairs that the seminars reshaped his thinking on the number of troops needed over the coming years.

“We are, as the Joint Chiefs and the combatant commanders, going through a series of strategic exercises now run by the chairman that helps us continue to sort through this and to make sure we are identifying all the issues that are out there,” Odierno said. At each of the sessions, the civilian leadership is represented by Ashton B. Carter, the deputy defense secretary.

Officials said the seminars, held at Marine Corps Base Quantico, in Virginia, are built around realistic scenarios for 2017. Like a traditional war game, they are chock-full of specifics about available troops and weapons, and with specific challenges to account for the tyranny of time, distance, weather and unexpected actions by the adversary.

But they also have aspects of a more academic seminar, in that the daylong events, the fourth of which is set for this month, invite differences of opinion — even disruptive thinking, participants say — while forcing the armed service chiefs who provide the personnel and weapons to work alongside the commanders who will use them in war.

The seminars, according to one senior participant, are “designed for us to ask uncomfortable questions about potential U.S. national military vulnerabilities in future conflicts” over the next five years.

“Given what we think potential adversaries can do, given what we think potential allies can do and given what we think we can do — do we need to make some changes?” said the senior official, who spoke on the condition of anonymity to give a sense of the intellectual and practical themes under discussion. “Let’s try to anticipate the future, to answer questions like, ‘How can we fight better? How could we fight differently? What new partners should we be seeking? How serious are the threats that we’re facing?”’

Dempsey described the new era through a medium that seemed to also define it — his Facebook page.

Discussing the first seminar, he wrote that it would “challenge our assumptions about the future security environment in 2017 and assess both the capability and the capacity of the Joint Force: that is, what can it do, how quickly, and for how long. I expect this seminar will produce a broad set of questions that will inform future seminars and eventually assist us in revising operational plans in execution of our strategy.”

© 2012 The New York Times Company