A drumbeat of demands to see the document has swelled on Capitol Hill in recent days as the Senate Intelligence Committee prepares to hold a confirmation hearing for John Brennan, who helped manage the drone program, to be CIA director.

Those demands were only intensified by the leak this week of an unclassified "white paper" on how decisions are made to target U.S. citizens abroad that the Justice Department confidentially sent to key lawmakers last year. The unclassified memo says it is legal for the government to kill U.S. citizens abroad if it believes they are senior al-Qaida leaders continually engaged in operations aimed at killing Americans, even if there is no evidence of a specific imminent attack.

The senior official said Obama decided to send lawmakers the classified rationale on Wednesday as part of his "commitment to consult with Congress on national security matters." Obama directed the Justice Department provide the Senate and House intelligence committees access to classified advice from its Office of Legal Counsel that the white paper is based on, the official said.

Legal opinions produced by the legal counsel's office are interpretations of federal law that are binding on all executive branch agencies.

The administration official spoke on condition of anonymity because he was not authorized to discuss the matter by name.

Earlier Wednesday, White House spokesman Jay Carney said Obama was engaged in an internal process deliberation to determine how to balance the nation's security needs with its values. He said Obama was committed to providing more information to Congress, even as he refused to acknowledge whether the drone memo even existed.

"He thinks that it is legitimate to ask questions about how we prosecute the war against al-Qaida," Carney said. "These are questions that will be with us long after he is president and long after the people who are in the seats that they're in now have left the scene."

Eleven senators, including Democrat Ron Wyden of Oregon, called on Obama to provide lawmakers "any and all legal opinions" that outline the president's authority to use legal force against Americans.

Wyden, a member of the Senate Intelligence Committee, told The Associated Press that Obama called him Wednesday evening to alert him to the decision to release the legal opinions. The president pledged to launch a "very extensive" public discussion on the government's ability to target Americans abroad, Wyden said.

"This is an encouraging first step," Wyden said. "There is now an opportunity to build on it."

Sen. Dianne Feinstein, D-Calif., committee's chairman, said in a statement that the legal opinion would be provided to her committee by Thursday morning. The confirmation hearing will be held Thursday afternoon.

Justice's unclassified 16-page white paper says that it is lawful to target al-Qaida linked U.S. citizens if they pose an "imminent" threat of violent attack against Americans and that delaying action against such people would create an unacceptably high risk. Such circumstances may necessitate expanding the concept of imminent threat, the memo says.

"The threat posed by al-Qaida and its associated forces demands a broader concept of imminence in judging when a person continually planning terror attacks presents an imminent threat," the document added.

A September 2011 drone strike in Yemen killed Anwar al-Awlaki and Samir Khan, both U.S. citizens. A separate drone strike two weeks later killed al-Awlaki's 16-year-old son, a Denver native. The strikes came after U.S. intelligence concluded that the elder al-Awlaki was senior operational leader of al-Qaida in the Arabian Peninsula plotting attacks on the U.S., including the abortive Christmas Day bombing of an airplane landing in Detroit in 2009.

The memo does not require the U.S. to have information about a specific imminent attack against the U.S. But it does require that capture of a terrorist suspect not be feasible and that any such lethal operation by the United States targeting a person comply with fundamental law-of-war principles.