A Senate hearing on the nomination of John O. Brennan to serve as CIA director exposed deep skepticism of key aspects of the Obama administration’s approach to fighting terrorism, including its unprecedented reliance on targeted killing and the secrecy it maintains around the exercise of that lethal power.

Brennan, who served as the White House’s top counterterrorism adviser for the past four years, was challenged in often blunt terms to explain why under President Obama the number of drone strikes has soared while captures of terrorism suspects have dwindled to single digits.

He was prodded to defend the administration’s refusal to provide basic information, including the death toll in drone strikes, and was asked to square his assertion that he opposed the CIA’s use of brutal interrogation measures with not trying to stop them while he was in the agency’s leadership ranks during the George W. Bush administration.

The hearing was one of the most heated sessions for a CIA nominee over the past decade, and a rare airing of lawmakers’ frustration with aspects of the way Obama has handled the conflict with al-Qaeda, if not its results.

Brennan delivered a confident and at times combative defense of his record and the administration’s decisions, and emerged from the session on course to be confirmed for the CIA job, perhaps as early as next week.

But Brennan, whose opening remarks were interrupted repeatedly by protesters in the audience, also expressed dismay with the way the administration’s actions have been perceived.

Defending the drone campaign, he said, “We only take such actions as a last resort, to save lives when there is no other alternative.” Protesters who were taken by police out of the hearing “have a misunderstanding of what we do as a government and the care that we take and the agony” that goes into decisions on lethal operations, he said.

Brennan added that he thinks U.S. officials “need to acknowledge it publicly” when civilians are killed in the drone campaign, something the administration has rarely, if ever, done.

Sen. Dianne Feinstein (D-Calif.), the chairman of the Senate intelligence committee, made it clear that she thinks the administration is a victim of its own secrecy.

Noting that she had sought permission to disclose government estimates of civilian casualties to bolster claims of the drones’ accuracy, Feinstein said she was told that “you can’t. It’s classified. For the public, [the drone campaign] doesn’t exist.”

“Well I think that rationale, Mr. Brennan, is long gone,” Feinstein said.

She also indicated, for the first time, that she plans to have the committee examine the creation of a special court to evaluate evidence against Americans who might be targeted, similar to the scrutiny applied to government monitoring of the communications of Americans suspected of having connections to terrorist groups.

Explore documented drone strikes in Pakistan, Yemen and Somalia

The hearing came just hours after the White House surrendered a set of Justice Department memos to the committee that lay out the legal rationale for killing U.S. citizens accused of serving as al-Qaeda operatives abroad.

The belated gesture appeared to have removed the main obstacle to Brennan’s confirmation among committee members.

The memos were not made public, and Sen. Ron Wyden (D-Ore.), who led the effort to acquire them, indicated that he thinks others are being withheld. But the hearing, combined with the leak on Monday of a government “white paper” summarizing the memos’ contents, pushed new details about the drone program into public view.

Brennan was confronted with repeated questions about his role as a senior CIA official when the agency began employing brutal interrogation techniques, including waterboarding, in the aftermath of the Sept. 11, 2001, attacks.

He acknowledged that he was “aware of the program” and reiterated that he expressed objections to associates at the time. But, he acknowledged, “I did not try to stop it,” saying that the program did not fall under his authority as deputy executive director.

The intelligence committee recently completed a 6,000-page classified report on the CIA’s interrogation program, which was disbanded when Obama took office.

Sen. Saxby Chambliss (Ga.), the ranking Republican on the panel, said the committee found at least 50 documents showing that Brennan had been copied on e-mails and other internal communications about the use of waterboarding and the results of harsh interrogations.

“We’ve not seen anybody . . . come forward to say they heard any objections from you,” the senator said. He and others said the administration’s decision to end the CIA’s detention program led to a surge in drone strikes instead.

The committee’s report, which concluded that harsh interrogation methods were not effective, also contains records that show that the program was “managed incompetently” and was “corrupted by personnel with pecuniary conflicts of interest,” said Sen. John D. Rockefeller IV (D-W.Va.).

Brennan, who said he had read a 300-page summary of the report, acknowledged that its contents had shaken his confidence in the agency’s assertions about how it was run.

In a 2007 interview, Brennan said the program had produced intelligence that had saved lives. “I must tell you that reading this report from the committee raises serious questions about the information that I was given at the time,” he said.

Still, Brennan resisted pressure from Democrats to describe the agency’s since-abandoned methods as torture. He also seemed to get tangled in the secrecy surrounding CIA operations even when allies on the committee were trying to help his case.

At one point, Feinstein asked a series of questions meant to make clear to the public that the only U.S. citizen intentionally killed in a drone strike was a deserving target. Anwar al-Awlaki, an American-born cleric, was killed in 2011 in Yemen.

Asked to describe Awlaki’s connections to deadly plots against the United States, Brennan said, “I would prefer not to at this time.”

Republican senators questioned Brennan repeatedly about his conversations with reporters during his White House tenure. Referring to leak investigations that are underway, Sen. James E. Risch (R-Idaho) stared at Brennan and said, “It seems to me that the leak the Justice Department is looking for is right in front of us.”

Brennan bristled, acknowledging that he had been interviewed in the inquiry but saying: “I’m not a subject, I’m not a target. I am a witness.”

If confirmed, Brennan would return to an agency that has been transformed over the past 12 years into a powerful paramilitary force. The CIA continues to collect intelligence from all corners of the world, but is increasingly focused on finding and striking al-Qaeda targets that are under near-constant surveillance by a growing fleet of armed drones.

Brennan voiced new concern about that direction for the agency, but offered no specifics on whether or how he might steer it back toward its traditional focus on intelligence collection and analysis.

Brennan would be the most experienced CIA director in decades. He worked at the agency for 25 years, rising from Middle East analyst and briefer to President Bill Clinton into the agency’s executive ranks.

After leaving government for a lucrative job with a government contractor, Brennan returned to serve as Obama’s counterterrorism adviser, a job that gave him such broad influence that some have suggested his move to the CIA would require him to relinquish power.

Julie Tate contributed to this report.