WASHINGTON — Nearly a dozen years after the hijackings that transformed America, President Obama said Thursday that it was time to narrow the scope of the grinding battle against terrorists and begin the transition to a day when the country will no longer be on a war footing.
Declaring that ‘‘America is at a crossroads,’’ the president called for redefining what has been a global war into a more targeted assault on terrorist groups threatening the United States. As part of a realignment of counterterrorism policy, he said, he would curtail the use of drones, recommit to closing the prison at Guantanamo Bay, and seek new limits on his own war power.
In a much anticipated speech at the National Defense University, Obama sought to turn the page on the era that began Sept. 11, 2001, when the imperative of preventing terrorist attacks became both the priority and the preoccupation.
Instead, the president suggested that the United States had returned to the state of affairs that existed before Al Qaeda toppled the World Trade Center, when terrorism was a persistent but not existential danger. With Al Qaeda’s core now ‘‘on the path to defeat,’’ he argued, the nation must adapt.
‘‘Our systematic effort to dismantle terrorist organizations must continue,’’ Obama said. ‘‘But this war, like all wars, must end. That’s what history advises. It’s what our democracy demands.’’
The president’s speech reignited a debate over how to respond to the threat of terrorism that has polarized the capital for years. Republicans contended that Obama was declaring victory prematurely and underestimating an enduring danger, while liberals complained that he had not gone far enough in ending what they see as the excesses of the Bush era.
The precise ramifications of his shift were less clear than the lines of argument, however, because the new policy guidance he signed remains classified, and other changes he embraced require congressional approval. Obama, for instance, did not directly mention in his speech that his new order would shift responsibility for drones more toward the military and away from the CIA.
But the combination of his words and deeds foreshadowed the course he hopes to take in the remaining 3½ years of his presidency to leave his successor a profoundly different national security landscape than the one he inherited in 2009. While President George W. Bush saw the fight against terrorism as the defining mission of his presidency, Obama has always viewed it as one priority among many at a time of wrenching economic and domestic challenges.
‘‘Beyond Afghanistan, we must define our effort not as a boundless ‘global war on terror,’ ’’ he said, ‘‘but rather as a series of persistent, targeted efforts to dismantle specific networks of violent extremists that threaten America.
‘‘Neither I, nor any president, can promise the total defeat of terror. We will never erase the evil that lies in the hearts of some human beings, nor stamp out every danger to our open society. But what we can do — what we must do — is dismantle networks that pose a direct danger to us, and make it less likely for new groups to gain a foothold, all the while maintaining the freedoms and ideals that we defend.’’
Some Republicans expressed alarm about Obama’s shift, saying it was a mistake to go back to the days when terrorism was seen as a manageable law enforcement problem rather than a dire threat.
‘‘The president’s speech today will be viewed by terrorists as a victory,’’ said Senator Saxby Chambliss of Georgia, the top Republican on the Senate Intelligence Committee. ‘‘Rather than continuing successful counterterrorism activities, we are changing course with no clear operational benefit.’’
Senator John McCain of Arizona said he still agreed with Obama about closing the Guantanamo prison, but he called the president’s assertion that Al Qaeda was on the run ‘‘a degree of unreality that to me is really incredible.’’
The liberal discontent with Obama was on display even before his speech ended. Medea Benjamin, a cofounder of the antiwar group Code Pink, who was in the audience, shouted at the president to release prisoners from Guantanamo, halt CIA drone strikes, and apologize to Muslims for killing so many of them.
‘‘Abide by the rule of law!’’ she yelled as security personnel removed her from the auditorium. ‘‘You’re a constitutional lawyer!’’
Colenel Morris D. Davis, a former chief prosecutor at Guantanamo who has become a leading critic of the prison, waited until after the speech to express disappointment that Obama was not more proactive.
‘‘It’s great rhetoric,’’ he said. ‘‘But now is the reality going to live up to the rhetoric?’’
Still, some counterterrorism experts saw it as the natural evolution of the conflict after more than a decade.
‘’This is both a promise to an end to the war on terror, while being a further declaration of war, constrained and proportional in its scope,’’ said Juan Carlos Zarate, a counterterrorism adviser to Bush.
The new classified policy guidance imposes tougher standards for when drone strikes can be authorized, limiting them to targets who pose ‘‘a continuing, imminent threat to Americans’’ and cannot feasibly be captured, according to government officials. The guidance also begins a process of phasing the CIA out of the drone war and shifting operations to the Pentagon.
The guidance expresses the principle that the military should be in the lead and responsible for taking direct action even outside traditional war zones like Afghanistan, officials said. But Pakistan, where the CIA has waged a robust campaign of air assaults on terrorism suspects in the tribal areas, will be grandfathered in for a transition period and remain under CIA control.