WASHINGTON — President Barack Obama on Thursday announced new restraints on targeted killings and narrowed the scope of the long struggle with terrorists as part of a transition to a day he envisions when the nation will no longer be on the war footing it has been on since the attacks of Sept. 11, 2001.
In a widely anticipated speech at the National Defense University, Obama offered his most expansive defense of the drone war he has waged since taking office, but he signaled that he planned to wind down the strikes, which have stirred controversy at home and abroad. He imposed a higher standard on authorizing such aerial attacks and shift responsibility more from the CIA to the military, and he suggested the creation of a secret court that would have to sign off on strikes in the future.
Obama also called on Congress to revise the authorization of force it passed in the aftermath of Sept. 11 to reflect the changing nature of the war on terrorism. And he renewed his moribund effort to close the prison at Guantanamo Bay, Cuba, by saying that he would lift a moratorium on transferring scores of detainees to Yemen.
Taken together, the president’s words and deeds added up to an effort to move the country away from the perpetual war on terrorism envisioned by his predecessor, George W. Bush, toward a more limited campaign against particular groups that would eventually be curtailed even if the threat of terrorism could never be eliminated.
''Our systematic effort to dismantle terrorist organizations must continue,’’ Obama said. ‘‘But this war, like all wars, must end. That’s what history advises. That’s what our democracy demands.’’
Obama rejected the notion of an expansive war on terrorism and instead articulated a narrower understanding of the mission for the US.
‘'Beyond Afghanistan, we must define our effort not as a boundless ‘global war on terror’ but rather as a series of persistent, targeted efforts to dismantle specific networks of violent extremists that threaten America,’’ he said.
''Neither I, nor any president, can promise the total defeat of terror,’’ Obama added. ‘‘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.’’
The president’s moves stirred immediate skepticism among Republicans, who have long questioned whether he was playing down the continuing threat of terrorism for political reasons, as in the case of the attack on the diplomatic post in Benghazi, Libya, last year.
House Speaker John A. Boehner, R-Ohio, issued 10 questions to the president in reaction to previews of his speech. ‘‘Is it still your administration’s goal to disrupt, dismantle, and defeat al-Qaida?’’ he asked. ‘‘If you are scaling back the use of unmanned drones, which actions will you be taking as a substitute to ensure al-Qaida’s defeat? Is it your view that if the US is less aggressive in eliminating terrorists abroad, the threat of terrorist attacks will diminish on its own?’’
Sen. Saxby Chambliss, R-Ga., the top Republican on the Intelligence Committee, was sharper in reaction. ‘‘The president’s speech today will be viewed by terrorists as a victory,’’ he said. ‘‘Rather than continuing successful counterterrorism activities, we are changing course with no clear operational benefit.’’
Some on the left were disappointed that he did not go further or that it had taken him so long to recommit to closing Guantanamo. Medea Benjamin, a co-founder of the activist group Code Pink, interrupted Obama’s speech, shouting that he should release Guantanamo detainees, stop 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!’’
Obama then went off script. ‘‘The voice of that woman is worth paying attention to,’’ he said. ‘‘Obviously I do not agree with much of what she said. And obviously she wasn’t listening to me and much of what I said. But these are tough issues. And the suggestion that we can gloss over them is wrong.’’
As part of its shift in approach, the administration on Wednesday formally acknowledged for the first time that it had killed four US citizens in drone strikes outside the battlefields of Afghanistan and Iraq, arguing that its actions were justified by the danger to the United States. Obama approved providing new information to Congress and the public about the rules governing his attacks on al-Qaida and its allies.
A new classified policy guidance signed by Obama will sharply curtail the instances when unmanned aircraft can be used to attack in places that are not overt war zones, countries like Pakistan, Yemen and Somalia. The rules will impose the same standard for strikes on foreign enemies now used only for US citizens deemed to be terrorists.
Lethal force will be used only against targets who pose ‘‘a continuing, imminent threat to Americans’’ and cannot feasibly be captured, Attorney General Eric H. Holder Jr. said in a letter to Congress, suggesting that threats to a partner like Afghanistan or Yemen alone would not be enough to justify being targeted.
''As our fight enters a new phase, America’s legitimate claim of self-defense cannot be the end of the discussion,’’ Obama said. ‘‘To say a military tactic is legal, or even effective, is not to say it is wise or moral in every instance. For the same human progress that gives us the technology to strike half a world away also demands the discipline to constrain that power — or risk abusing it.’’
The new standard could signal an end to ‘‘signature strikes,’’ or attacks on groups of unknown men based only on their presumed status as members of al-Qaida or some other enemy group — an approach that administration critics say has resulted in many civilian casualties. Although officials did not explicitly rule out such strikes in the future, they said the requirements for authorizing them were increased and the need for them was reduced.
As part of the shift, the president has decided that the military should take over the drone program from the CIA. In briefing reporters on the condition of anonymity on Thursday, an official said that the CIA would not necessarily give up involvement in such strikes, but that ‘‘the preference’’ would be for the military to have ‘‘the lead for the use of force not just in war zones like Afghanistan but beyond Afghanistan, where we are fighting al-Qaida and associated forces.’’
The CIA, which has overseen the drone war in the tribal areas of Pakistan and elsewhere, will generally cede its role to the military after a six-month transition period as forces draw down in Afghanistan, other officials said Wednesday. Drone strikes have already been decreasing in the past few years as targets have been killed and opposition has grown.
John O. Brennan, the new CIA director, has been eager to shift the agency more toward espionage, intelligence gathering and analysis and away from the paramilitary mission it has adopted since Sept. 11.
The changes reflect a conclusion by the White House that the core of al-Qaida has been decimated by years of strikes and the raid that killed Osama bin Laden. But in the speech, the president said that the threat had evolved in a complicated mosaic of dangers from affiliated groups and homegrown terrorists, like the bombers who attacked the Boston Marathon.
The president had been planning to deliver the speech for months to address criticism from both left and right, hoping, according to aides, to acknowledge more explicitly than ever before the complicated trade-offs and legitimate debate that his policies had provoked. But he hoped to make the case that his drone strikes had caused far fewer civilian casualties than traditional and less discriminate military force.
The president embraced the idea of a secret court to oversee drone strikes, much like the intelligence court that authorizes secret wiretaps, or instead perhaps some sort of independent body within the executive branch. He did not outline a specific proposal, but left it to Congress to consider something along those lines.
He also weighed in on the dispute over the Justice Department’s seizure of journalists’ phone and email records in pursuing national security leak investigations. He said he had talked with Attorney General Eric H. Holder Jr., who agreed to review department guidelines and meet with media executives and report back by July 12.
''I am troubled by the possibility that leak investigations may chill the investigative journalism that holds government accountable,’’ Obama said. ‘‘Journalists should not be at legal risk for doing their jobs.’’
In renewing his vow to close the Guantanamo prison, Obama highlighted one of his most prominent unkept promises. He came into office promising to shutter the facility, which has been a symbol around the world of US excesses, within a year, but Congress moved to block him, and he then largely dropped the effort.
With 166 detainees still at the prison, Obama said he would take what steps he could with his own authority to reduce the population. The largest group of detainees remaining is from Yemen, and he decided to lift the moratorium he imposed on transferring those prisoners back to their home country.
The moratorium was first enacted because of the volatile nature of the government in Yemen and the fear that prisoners would be released and rejoin terrorist groups targeting the US But with a new president in Yemen, Abdu Rabbu Mansour Hadi, one White House official said the United States now ‘‘has a willing and increasingly able partner,’’ and so the president felt assured enough to resume transfers.
Obama will also appoint a new high-level State Department official to replace Dan Fried, who oversaw the effort to reduce the Guantanamo prison population in the first term, and the president will also assign a top official at the Defense Department to work toward the goal.
Republicans reacted cautiously, saying that Obama had not been serious about proposing a credible alternative to Guantanamo.
''I am open to a proposal from the president regarding Guantanamo Bay, but that plan has to consist of more than political talking points,’’ said Rep. Howard ‘‘Buck’’ McKeon, R-Calif., the chairman of the House Armed Services Committee. ‘‘The president doesn’t need to remind Americans that Guantanamo is an imperfect solution, we all know that. He must offer solid answers about what he thinks is a better option.’’