Some of the practices produced revulsion among some in Congress and the public, but the outcry has been muted because Brennan and others have said these harsh and secretive methods saved American lives.
Those issues will be front and center in the Senate Intelligence Committee hearing today for Brennan -- a chance for him to answer criticism that he backed the detention and interrogation policy while he served at the CIA under President George W. Bush, charges that stymied his first attempt to head the intelligence agency in 2008.
In answers to questions from the Senate Intelligence Committee before the hearing, Brennan said he was "aware of the program but did not play a role in its creation, execution, or oversight," and added that he "had significant concerns and personal objections" to the interrogation techniques.
He wrote that he voiced those objections to colleagues at the agency privately.
Brennan also described how individuals are targeted for drone strikes, saying whether a suspect is deemed an imminent threat -- and therefore appropriate for targeting -- is made "on a case-by-case basis through a coordinated interagency process" involving intelligence, military, diplomatic and other agencies.
He defended the missile strikes by Predator or Reaper drones as a more humane form of war. Aides have portrayed him as cautious in their use, restraining others at the CIA or military who would use them more often, even though as the White House's counterterror czar he has presided over an explosion of drone strikes in Pakistan, Yemen and Somalia. Less than 50 strikes took place during the Bush administration while more than 360 strikes have been launched under President Barack Obama, according to the website The Long War Journal, which tracks the casualties.
Administration officials said Brennan would further limit the use of drones by the CIA and leave the majority of strikes to the military.
CIA drone strikes primarily focus on al-Qaida and Taliban targets in the tribal regions of Pakistan, while the military has launched strikes against al-Qaida targets in Yemen and Somalia.
The CIA also carries out strikes in Yemen from a base in Saudi Arabia, including one that killed three American citizens. The location of the base was first disclosed by The New York Times in a story that previewed Brennan's hearing, highlighting the sensitive issues the hearings will bring into the open.
Democrats in Congress have begun to express stronger opposition to the use of drones, but on Wednesday Obama found an ally in Republican Sen. Lindsey Graham, who expressed his "100 percent" support of the use of drones against terror suspects.
Brennan will face questions about charges that White House officials leaked details of national security policies, including its cyberattacks against Iran's nuclear infrastructure, to burnish Obama's standing as commander in chief before last year's presidential election. Brennan has come under fire by Republican lawmakers who believe he gave the media too many details after the 2011 killing of al-Qaida mastermind Osama bin Laden.
The Obama White House launched a sweeping investigation led by two Justice Department lawyers in response to congressional ire over the leaks. White House officials have defended briefings given by Brennan as authorized and backed by the president, who they say has the ultimate authority to declassify information.
Brennan told the Senate committee in his written answers that he was questioned as a voluntary witness in the leak investigation. He also said that in his current role he is "vigilant about not disclosing classified intelligence matters with unauthorized persons, including reporters and media consultants."
House Intelligence Committee Chairman Mike Rogers, R-Mich., who has strongly criticized the administration's release of information on its national security programs, predicted "lots of questions about leaks and detention" at the Senate hearings, but he also predicted that Brennan would ultimately be confirmed.
When he joined the White House as the top counterterrorism advisor in 2009, Brennan publicly decried the interrogation practices, saying they backfired and produced more terrorists, leading him to urge the newly elected president to stop them.
That represented an evolution from earlier statements to the media.
In a CBS News interview in 2007, Brennan acknowledged that the practices came close to torture, but he seemed to defend them. "There has been a lot of information that has come out from these interrogation procedures that the agency has, in fact, used against the real hard-core terrorists," Brennan said. "It has saved lives."
Brennan told the committee in his written responses that "a lot of information, both accurate and inaccurate, came out of interrogation sessions conducted by (the) CIA," but that he believed the techniques were legal but "counterproductive."
"These techniques would not be used again by the CIA if I were the director," he wrote.
Brennan moved from his job as deputy executive CIA director in 2003 to become director of the Terrorist Threat Integration Center, and then interim director of its next incarnation, the National Counterterrorism Center. When Bush's second term began, Brennan left government to run The Analysis Corp., which provides counterterror analysis to government agencies, from 2005 to 2008. After Obama's election, he returned to the government payroll, in 2009, as the White House counterterror czar, where he made public his views on harsh interrogation.
Brennan was nominated to replace CIA director David Petraeus, who resigned late last year, citing an extramarital affair.
Sen. Dianne Feinstein, D-Calif., chairwoman of the Senate Intelligence Committee, has signaled she will support Brennan's nomination, but congressional staffers say both she and her Republican counterparts will ask Brennan to explain publicly if he objected to the interrogation program, and whether he believes it produced any useful intelligence.
Feinstein's committee just produced a 6,000-page classified report on the interrogation program that says it did not. Congressional aides said she would seek Brennan's support in future, if the committee votes to declassify portions of it after the White House and CIA finish reviewing the document.
Feinstein and others will also keep pressing Brennan and the White House to show them the classified legal memo that outlines specifically when drones and other lethal strikes can be employed against al-Qaida. An unclassified Justice Department White Paper was made public this week, outlining America's authority to kill suspected terrorists with drones, even U.S. citizens, if a case can be made by the CIA or military that they are linked to al-Qaida and have taken part in plots against Americans.
AP National Security Correspondent Lara Jakes and Associated Press writer Donna Cassata contributed to this report.
Dozier can be followed on Twitter (at) kimberlydozier.