A Justice Department document describes the criteria for killing American citizens believed to be plotting terror attacks from abroad. The Post’s Karen DeYoung helps explain what the “white paper” does and doesn’t says. (The Fold/The Washington Post)

President Obama’s plan to install his counterterrorism adviser as director of the CIA has opened the administration to new scrutiny over the targeted-killing policies it has fought to keep hidden from the public, as well as the existence of a previously secret drone base in Saudi Arabia.

The administration’s refusal to provide details about one of the most controversial aspects of its drone campaign — strikes on U.S. citizens abroad — has emerged as a potential source of opposition to CIA nominee John O. Brennan, who faces a Senate confirmation hearing scheduled for Thursday.

The secrecy surrounding that policy was punctured Monday with the disclosure of a Justice Department “white paper” that spells out the administration’s case for killing Americans accused of being al-Qaeda operatives.

The timing of the leak appeared aimed at intensifying pressure on the White House to disclose more-detailed legal memos that the paper summarizes — and at putting Brennan, Obama’s top counterterrorism adviser, on the defensive for his appearance on Capitol Hill.

Administration officials on Tuesday sought to play down the significance of the disclosure, saying that they have already described the principles outlined in the document in a series of speeches.

Drones and spy planes over Africa

“One of the things I want to make sure that everybody understands is that our primary concern is to keep the American people safe, but to do so in a way that’s consistent with our laws and consistent with our values,” Attorney General Eric H. Holder Jr. said in response to questions about the document.

Nevertheless, the leak and signals from senior lawmakers that they may seek to delay, if not derail, Brennan’s confirmation made it clear that Obama’s decision to nominate him has drawn the White House into a fight it had sought to avoid.

Sen. Ron Wyden (D-Ore.), a member of the intelligence committee, said Brennan’s level of influence and the timing of his nomination have given lawmakers leverage that they lacked in previous efforts to seek details from the White House.

Brennan “is the architect of [the administration’s] counterterrorism policy,” Wyden said. “If the Congress doesn’t get answers to these questions now, it’s going to be extremely difficult, if not impossible, to get them in the future.”

The Obama administration’s targeted-killing program has relied on a growing constellation of drone bases operated by the CIA and the U.S. military’s Joint Special Operations Command. The only strike intentionally targeting a U.S. citizen, a 2011 attack that killed al-Qaeda operative Anwar al-Awlaki, was carried out in part by CIA drones flown from a secret base in Saudi Arabia.

The base was established two years ago to intensify the hunt against al-Qaeda in the Arabian Peninsula, as the affiliate in Yemen is known. Brennan, who previously served as the CIA’s station chief in Saudi Arabia, played a key role in negotiations with Riyadh over locating an agency drone base inside the kingdom.

The Washington Post had refrained from disclosing the specific location at the request of the administration, which cited concern that exposing the facility would undermine operations against an al-Qaeda affiliate regarded as the network’s most potent threat to the United States, as well as potentially damage counterterrorism collaboration with Saudi Arabia.

Explore documented drone strikes in Pakistan, Yemen and Somalia

The Post learned Tuesday night that another news organization was planning to reveal the location of the base, effectively ending an informal arrangement among several news organizations that had been aware of the location for more than a year.

The white paper, which was first reported by NBC News, concludes that the United States can lawfully kill one of its own citizens overseas if it determines that the person is a “senior, operational leader” of al-Qaeda or one of its affiliates and poses an imminent threat.

But the 16-page document allows for an elastic interpretation of those concepts and does not require that the target be involved in a specific plot, because al-Qaeda is “continually involved in planning terrorist attacks against the United States.”

The paper does not spell out who might qualify as an “informed, high-level official” able to determine whether an American overseas is a legitimate target. It avoids specifics on a range of issues, including the level of evidence required for an American to be considered a “senior, operational” figure in al-Qaeda.

The document’s emphasis on those two words, which appear together 16 times, helps to explain the careful phrasing the administration employed in the single case in which it intentionally killed an American citizen in a counterterrorism strike.

Within hours after Awlaki’s death in September 2011, White House officials described the U.S.-born cleric as “chief of external operations” for al-Qaeda’s affiliate in Yemen, a designation they had not used publicly before the strike.

Officials said that Awlaki, previously portrayed mainly as a propagandist, was directly involved in a series of plots, including the attempted bombing of a Detroit-bound airliner on Christmas Day in 2009.

The white paper, which was distributed confidentially to certain lawmakers last summer, does not indicate when the underlying Justice Department memos on targeted killings of Americans were completed.

As a result, it is unclear whether the memos were in place before the first apparent attempt to kill Awlaki, a joint U.S.-Yemeni strike shortly before the foiled Detroit plot in 2009.

Three other Americans have been killed in U.S. airstrikes in Yemen since 2002, including Awlaki’s 16-year-old son. U.S. officials have said those Americans were casualties of attacks aimed at senior al-Qaeda operatives.

Civil liberties groups described the white paper as an example of the kind of unchecked executive power Obama campaigned against during his first presidential run.

“The parallels to the Bush administration torture memos are chilling,” said Vincent Warren, executive director of the Center for Constitutional Rights. Warren accused Obama of hypocrisy for ordering George W. Bush administration memos to be released publicly while maintaining secrecy around his own. To deliver on his promises of transparency, Warren said, Obama “must release his own legal memos and not just a Cliffs Notes version.”

White House press secretary Jay Carney emphasized that the white paper is unclassified and indicated that the administration does not intend to release the classified legal memo on which it is based. Asked whether Obama would respond to demands from lawmakers that he release the original document, Carney said, “I just have nothing for you on alleged memos regarding potentially classified matters.”

The number of attacks on Americans is minuscule compared with the broader toll of the drone campaign, which has killed more than 3,000 militants and civilians in hundreds of strikes in Pakistan, Yemen and Somalia.

The administration has frequently described its domestic and international legal rationales for drone strikes in general terms. The white paper expands those justifications with specific determinations to be made in the case of U.S. citizens.

The struggle between the administration and Congress is relatively narrow, limited mainly to the White House’s refusal to turn over a collection of classified memos rather than any broad-scale opposition to the use of drone strikes or even the killing of Americans.

Most members of Congress agree with administration assertions that the drone campaign has been essential to crippling al-Qaeda and its ability to mount large-scale attacks against the United States.

Sen. Dianne Feinstein (D-Calif.), the chairman of the intelligence committee that will consider Brennan’s nomination, released a statement Tuesday indicating that she believes the release of the white paper — which was apparently done without the consent of the administration — should quell calls for more transparency.

The administration’s legal position “is now public and the American people can review and judge the legality of these operations,” Feinstein said. She has indicated she will support Brennan’s nomination.

Brennan, 57, has presided over a major expansion of the drone campaign, although he is also credited with imposing more rigorous internal reviews on the selection of targets. He spent 25 years at the CIA and was considered a likely candidate for the top job in Obama’s first term. He withdrew amid mounting opposition from civil liberties groups that called attention to his role as a senior CIA executive when the agency began using interrogation techniques, including waterboarding, that were subsequently denounced as akin to torture.

Julie Tate contributed to this report.