Former and current U.S. intelligence officials who were part of those briefings say Brennan, then deputy executive director of the CIA's administrative arm, did not raise objections to the interrogation practices in those forums.
They spoke on condition of anonymity because they are not authorized to discuss the top-secret meetings publicly.
Brennan's silence may have cost him his first chance to lead the spy agency. He withdrew his name from consideration in 2008 following a stream of complaints that he was tainted by his CIA service during the administration of President George W. Bush, when harsh interrogation techniques like waterboarding came under fire.
But in his letter withdrawing his nomination, Brennan wrote that he'd been a "strong opponent" of the program.
Throughout Obama's first term, Brennan added to the body of criticism of so-called enhanced interrogation techniques in his role as Obama's counterterrorism adviser.
The same issue that caused him to withdraw from consideration to be the nation's spy chief is likely to come up again this week as Brennan faces his confirmation hearings in Congress to be director of the CIA.
Brennan declined to be interviewed, as is customary ahead of confirmation hearings.
A senior administration official speaking on Brennan's behalf said Brennan had "significant concerns and personal objections to many elements of the EIT program while it was under way. He voiced those objections privately with colleagues at the agency."
The official, speaking on condition of anonymity because he wasn't authorized to discuss the nomination publicly, said Brennan spoke out after being named to his current job, where he was "in a position of influence over decisions such as how we handle interrogations, and he advised the president to ban such techniques."
Brennan is likely to be quizzed on his desire to stop the CIA from conducting drone strikes on terror suspects and leave that to the military. He will also probably be asked about a growing feeling in Congress that the administration has too much authority to kill terror suspects, including U.S. citizens.
Some of the former and current U.S. intelligence officials said he was silent during the Bush administration because it wasn't his place to object to a White House-approved policy that was run by another CIA department.
Others said he could have objected to any subject raised at any briefing in keeping with CIA custom.
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.
"Tactics such as waterboarding were not in keeping with our values as Americans, and these practices have been rightly terminated and should not and will not happen again," Brennan said in an August 2009 speech to the Center for Strategic and International Studies. But Brennan's previous public statements suggest he may have felt the program was both necessary, and useful, at the time.
Waterboarding is a technique in which interrogators typically wrap a cloth over a restrained suspect's face and pour water on the cloth at timed intervals to simulate the sensation of drowning.
In a 2006 interview with the PBS program "Frontline," Brennan said, "When it comes to individuals who are determined to destroy our nation, though, we have to make sure that we take every possible measure."
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."
But in his first year in the Obama White House, Brennan offered a different view.
"Such practices not only fail to advance our counterterrorism efforts, they actually set back our efforts," he said in the 2009 speech. "They are a recruitment bonanza for terrorists, increase the determination of our enemies and decrease the willingness of other nations to cooperate with us."
One close associate of Brennan said his thinking evolved, as did that of many in the intelligence service.
Panicked strategy sessions where CIA officers grasped at untried methods to speed up the intelligence cycle, under the pressure of the threat of another 9/11-style attack, gave way to the longer war. That second major attack did not materialize, and U.S. intelligence officials saw the news reports of harsh interrogation used against the U.S., fueling militant jihadist recruitment drives.
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 how, 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.
The CIA program authorized intelligence officers to capture al Qaeda suspects and hold them around the world without charge, and interrogate them using techniques such as sleep deprivation and waterboarding,
The California senator wants the White House's support to declassify part of the document and let it become part of the argument against the program, congressional aides said, speaking on condition of anonymity because they were not authorized to speak publicly. The administration and the CIA are both reviewing the report.
Feinstein has also demanded that the CIA share evidence backing up public statements that the program helped track down terrorist leader Osama bin Laden - proof she said her investigators could not find in the agency's report.
Sen. Ron Wyden, D-Ore., a member of the Intelligence Committee, also asked Brennan to react "to the report's revelation that the CIA repeatedly provided inaccurate information about its interrogation program to the White House, the Justice Department and Congress."
"This is about how Brennan will lead. What is he going to do about the fact that the White House and the Congress were lied to?" said Andrea Prasow, senior counterterrorism counsel at Human Rights Watch. "A commitment to disclosing that study will go a long way to showing he wants oversight."
Sen. Mark Udall, D-Colo., complained that Brennan would not go into the subject in a closed-door meeting with senators last week.
"He hadn't reviewed the report at all," but promised to review it before Thursday's hearings, Udall said.
"I understand that he may not see it in his or the CIA's interests to criticize the very agency that he hopes to lead, but I see this as an opportunity for Mr. Brennan to correct the record."
Among those listening closely to how Brennan explains his evolving statements to the senators will be CIA officers past and present, including those who helped craft the interrogation program.
John McLaughlin, who served as acting CIA director during Brennan's CIA tenure, said if asked, Brennan won't hold back or sugarcoat.
"John and I were discussing how to share a really difficult piece of news with the president," McLaughlin said of a conversation with Brennan during their time at the CIA. "John said, 'My dad always said the best policy is to tell the truth.' So that's what we did."