WASHINGTON » The pivot in counterterrorism policy that President Barack Obama announced last week was nearly two years in the making, but perhaps the most critical moment came last spring during a White House meeting as he talked about the future of the nation’s long-running terrorism war. Underlying the discussion was a simple fact: It was an election year. And Obama might lose.

For nearly four years, the president had waged a relentless war from the skies against al-Qaida and its allies, and he trusted that he had found what he considered a reasonable balance even if his critics did not see it that way. But now, he told his aides, he wanted to institutionalize what in effect had been an ad hoc war, effectively shaping the parameters for years to come "whether he was re-elected or somebody else became president," as one aide said.

Ultimately, he would decide to write a new playbook that would scale back the use of drones, target only those who really threatened the United States, eventually get the CIA out of the targeted killing business and, more generally, begin moving the U.S. past the "perpetual war" it had waged since Sept. 11, 2001. Whether the policy shifts will actually accomplish that remains to be seen, given vague language and compromises forced by internal debate, but they represent an effort to set the rules even after he leaves office.

"We’ve got this technology, and we’re not going to be the only ones to use it," said a senior White House official, who, like others involved, declined to be identified talking about internal deliberations. "We have to set standards so it doesn’t get abused in the future."

While part of the re-evaluation was aimed at the next president, it was also about Obama’s own legacy. What became an exercise lasting months, aides said, forced him to confront his deep conflicts as commander in chief: the Nobel Peace Prize winner with a "kill list," the anti-war candidate turned war president, the avowed champion of transparency ordering operations over secret battlegrounds. He wanted to be known for healing the rift with the Muslim world, not raining down death from above.

Over the past year, aides said, Obama spent more time on the subject than on any other national security issue, including the civil war in Syria. The speech he would eventually deliver at the National Defense University became what one aide called "a window into the presidential mind" as Obama essentially thought out loud about the trade-offs he sees in confronting national security threats.

"Americans are deeply ambivalent about war," the president said in his speech, and he seemed to be talking about himself as well. Obama said the seeming precision and remote nature of modern warfare can "lead a president and his team to view drone strikes as a cure-all for terrorism," and it was not hard to imagine which president he had in mind.

"We must define the nature and scope of this struggle," Obama said, "or else it will define us."

In a sense, that had already happened to Obama. Somehow he had gone from the candidate who criticized what he saw as President George W. Bush’s excesses to the president who expanded the drone program his predecessor had left him. The killing he authorized in September 2011 of Anwar al-Awlaki, an American citizen tied to terrorist attacks, brought home the disparity between how he had envisioned his presidency and what it had become. Suddenly, a liberal Democratic president was being criticized by his own political base for waging what some called an illegal war and asserting unchecked power.The Awlaki strike also killed another American, Samir Khan, who officials say was not intentionally targeted. A subsequent strike killed Awlaki’s 16-year-old American son, a death that officials say was an accident. A furor over the American deaths convinced Obama that it was time to lay out clearer standards and practices for drone warfare.

Under the stewardship of John O. Brennan, then the president’s counterterrorism adviser, officials spent months discussing how to be more transparent about a program that was still officially secret and how to define its limits. After last spring’s discussion with the president, Brennan began a more intensive, formalized interagency process to rewrite the rules. He also took a first step in explaining the administration’s drone policy to the public with a speech, in which he said strikes targeted only those who pose "a significant threat to U.S. interests." But even then he did not acknowledge Awlaki’s killing.

In seemingly endless meetings, including a dozen or more with the president, Brennan and other administration officials grappled with the issue. Concluding that al-Qaida’s core leadership had been decimated, some officials wanted tighter restrictions on the use of drone strikes, but the CIA and the Pentagon balked. The CIA’s counterterrorism center resisted another proposal to take its drones away and put them under Pentagon control.

While the agencies argued, Obama focused on winning a second term, boasting about the same aggressive approach he was privately rethinking. "Ask Osama bin Laden and the 22 out of 30 top al-Qaida leaders who’ve been taken off the field whether I engage in appeasement," he said in response to campaign criticism. Days after his victory, though, he told his staff he wanted to conclude the review with a major speech, although there would no longer be pressure to complete it before the next inauguration, since he would be staying. Around the White House, it became known as Archives 2, a reference to the president’s May 2009 speech at the National Archives on counterterrorism issues.

"What he said repeatedly is he felt when he took office it wasn’t clear how we used this tool," said Benjamin J. Rhodes, the deputy national security adviser assigned to write the speech. "Part of this frankly is laying out for the American people but also for the next president: Here’s how we do this."

The first outlines of the speech came together in February. But there were critical debates to resolve. As Brennan departed to become CIA director, his replacement, Lisa Monaco, and the top White House national security lawyer, Avril D. Haines, ushered the process to a conclusion.

Ultimately, the president and his team decided to tighten the standard for which targets could be struck outside overt war zones. Instead of being authorized for any "significant threat to U.S. interests," drone strikes would be used only in cases of a "continuing and imminent threat to U.S. persons." They would also be limited to cases with a "near certainty" of avoiding civilian casualties.

The CIA’s opposition to shifting responsibility for drones entirely to the Pentagon resulted in a compromise: There would be a transition period for the program in Pakistan, which would be reviewed every six months to determine if it was ready to be moved to military control. Administration officials suggest that the transfer of the Pakistan drone program may coincide with the withdrawal of combat troops from Afghanistan in 2014.

"The hawks may be grumbling about it, but that’s to be expected," said a senior government official who supported the strategy shift. "This is a big change. But no one is screaming."

The hawks proposed a change of their own, suggesting as The Daily Beast has reported that the president leave individual strike decisions to the Pentagon and the CIA. But the White House rejected that. Obama felt those decisions were the president’s responsibility: He wanted to keep his own finger on the trigger.

All of that was codified in a Presidential Policy Guidance that remains classified. To address drone policy, though, meant owning up to the killings of Awlaki and other Americans, officials concluded. The CIA and others resisted, but Obama decided to declassify information about not just Awlaki’s killing, but the killings of his son, Khan and one other American who officials also say had not been intentionally targeted.

Obama was also interested in instituting an independent review of how and when drone strikes would be conducted. Multiple papers were prepared and multiple options evaluated. Among them was a special court to oversee targeted killings, but the discussion became tied up in knots about how it would work. Would a judge have to approve such strikes in advance or after the fact? What about an independent board within the executive branch instead? Administration lawyers argued against surrendering presidential authority, and defense policymakers argued against giving up operational control.

That proved to be a debate Obama could not resolve. In his speech, he invited Congress to come up with ideas. He also thought it was time to review the authorization of force that Congress passed in the days after Sept. 11, 2001, and that has been the legal foundation for the war on terrorism. But after a two-hour discussion just days before the speech, he could not decide exactly how to do that either.

In the midst of the White House debate, two bombs went off at the Boston Marathon in an attack attributed to two ethnic Chechens living legally in the U.S., reaffirming the continuing threat of terrorism. For Obama, it was another pivot point. The Boston attack, he thought, typified the new terrorist threat more than 11 years after Sept. 11, 2001: smaller-scale attacks that have fewer casualties but are harder to stop and often conducted by people radicalized in the U.S.

At the beginning of May, Rhodes, the national security official, gave Obama a first draft of the speech, but the president tossed it out and wrote out a detailed outline by hand over several pages.

Obama expanded it from drones to include a renewal of his failed promise to close the prison at Guantanamo Bay, Cuba. He also wanted fresh emphasis on nonmilitary tools like diplomacy, foreign aid and helping other countries deal with the threats inside their borders, although he made sure the word "patiently" was added to reflect the difficulty.

Some Pentagon and State Department officials learned only the day before the speech that Obama would lift his moratorium on repatriating Guantanamo detainees to Yemen and appoint a new official at the Defense Department to oversee transfer efforts.

Obama’s eventual speech, at 59 minutes one of the longest of his presidency other than a State of the Union address, reflected the process that developed it. Even as he set new standards, a debate broke out about what they actually meant and what would actually change. For now, officials said, "signature strikes" targeting groups of unidentified armed men presumed to be extremists will continue in the Pakistani tribal areas.

Even as he talked about transparency, he never uttered the word "CIA" or acknowledged he was redefining its role. He made no mention that a drone strike had killed an American teenager in error. While he pledged again to close the Guantanamo prison, he offered little reason to think he might be more successful this time.

Yet even the promise of change left some people scathingly critical. "At the end of the day," said Sen. Lindsey Graham, a South Carolina Republican, "this is the most tone-deaf president I ever could imagine, making such a speech at a time when our homeland is trying to be attacked literally every day."