At least three other Americans, including Awlaki’s 16-year-old son, and an estimated 3,500 other people have been killed in drone attacks since 2003.

Brennan vigorously defended the program, saying that targets are selected through a rigorous review procedure based on accurate intelligence. Strikes, he said, are ordered only as “a last resort” after a determination that terrorists are beyond capture. He insisted that the strikes are designed to prevent imminent terrorist attacks, not to avenge past operations.

“Any actions we take fully comport with our law,” he said, pushing back on charges by some prominent legal scholars and civil and human rights groups that the program is unconstitutional.

Sen. Dianne Feinstein, D-Calif., the panel’s chairwoman, who for more than a year has called on the administration to make public more information on targeted killings, said the panel has “done significant oversight” that has verified the administration’s claims that annual civilian casualties have “typically been in the single digits.”

But she complained that the administration is still withholding eight legal opinions pertaining to the program and said that the administration had prevented the committee’s staff from reading the Justice Department opinion that had been given to the committee ahead of the hearing.

Asserting that he was a proponent of greater transparency, Brennan said that he would advocate the release of those documents to the committee.

Feinstein was joined by other lawmakers in questioning Brennan about the CIA’s use on al Qaida detainees of waterboarding, sleep deprivation and other harsh interrogation practices that many experts consider torture and which were adopted after the Sept. 11, 2001, attacks. At the time, Brennan served as a senior CIA executive.

Brennan reiterated that while he was aware of the program, he was not involved in it and wasn’t in a position to halt the practices. He insisted that he had raised his “personal objections” in conversations with other top officials.

But Sen. Saxby Chambliss of Georgia, the panel’s senior Republican, seemed to question Brennan’s assertion, saying that the committee has 50 emails concerning the program – and the information it produced –that Brennan had received. He added that none of Brennan’s former colleagues could recall his objecting to the program.

“I was copied on thousands upon thousands . . . of e-mail distributions,” Brennan said.

He declined several times to describe waterboarding as torture, but he agreed that it is “reprehensible and something that should not be done.” Obama banned the use of the procedure and other hard techniques after he took office in 2009.

The hearing provided new insights into a classified six-year, 6,000-page report by the committee on the interrogation program, with several senators saying that it found CIA officials misrepresented the information produced from the use on al Qaida detainees of waterboarding and other harsh interrogation techniques.

“There can never be that kind of situation again, where . . . we have to tell you what’s going wrong in your agency,” said Sen. Jay Rockefeller, D-W.Va., who added that the program was “executed by personnel without relevant experience, managed incompetently by senior officials who did not pay attention to crucial details, and corrupted by personal and pecuniary conflicts of interest.”

“It was sold to policymakers and lawyers of the White House, the Department of Justice and Congress, with grossly inflated claims of professionalism and effectiveness, so-called lives saved,” he said.

Brennan was pressed several times on whether he concurred with former senior CIA officials who insist that the methods had produced intelligence that led to the location and death of Osama bin Laden in a Navy SEAL raid in May 2011, or if he accepted the report’s findings that they had not.

He conceded that during that period he had believed that the interrogations produced “valuable information” but was shocked by the report’s revelations. But he declined to say whether he accepted its conclusions, saying he first wanted a chance to review the CIA’s rebuttal.