WASHINGTON - Civil and human rights advocates on Tuesday denounced a leaked Obama administration "white paper" that sets out the legal justification for killing U.S. citizens suspected of being members of Al-Qaida, an issue certain to arise during Thursday's confirmation hearing of White House counterterrorism adviser John Brennan to be CIA director.

The White House defended the practice of targeted killing, for which Brennan is a key overseer, as "legal, ethical and wise." But spokesman Jay Carney rejected anew calls from some lawmakers, including Minnesota Sen. Al Franken, for the release of a 2010 Justice Department legal opinion on which the administration has based its use of unmanned drones to target Americans it accuses of being affiliated with Al-Qaida, most notably Anwar al-Awlaki, the spiritual leader of Al-Qaida's Yemen affiliate.

The 16-page Justice Department white paper became public late Monday after it was leaked to NBC. It asserts that the government has the constitutional power to kill a U.S. citizen who is believed to be a leader of Al-Qaida or an "associated force" and is in another country "actively engaged in planning operations to kill Americans."

The memo says three conditions must be met: "An informed, high-level official of the U.S. government has determined that the targeted individual poses an imminent threat of violent attack against the United States; (2) capture is infeasible ... and (3) the operation would be conducted in a manner consistent with applicable law of war principles."

Civil and human rights experts said the paper jumbles international and U.S. law. They also rejected the administration's assertion that the president's sweeping authority to kill Americans abroad is beyond court review as well as what they called an exaggerated rewrite of the legal definition of imminent threat. "The government just gets to make decisions in secret," said Andrea Prasow, senior counterterrorism counsel for Human Rights Watch.

But the administration received a vote of confidence from Rep. Mike Rogers, R-Mich., a former FBI agent who chairs the House Intelligence Committee. "I agree with the Justice Department's conclusion that targeting a senior leader of Al-Qaida is a lawful act of national self-defense in these circumstances," Rogers said. "When an individual has joined Al-Qaida -- the organization responsible for the murder of thousands of Americans -- and actively plots future attacks against U.S. citizens, soldiers and interests around the world, the U.S. government has both the authority and the obligation to defend the country against that threat."

Targeted killing, which began under former President George W. Bush, is a classified CIA program. It is known to involve only missile strikes by unmanned aircraft in Pakistan, Somalia and Yemen against what U.S. officials say are leaders of Al-Qaida and "associated groups" plotting imminent attacks on U.S. targets.

An estimated 3,500 people have been killed in the strikes, the vast majority in Pakistan's tribal area bordering Afghanistan, a region largely outside government control where Al-Qaida and allied militants have found sanctuary.

At least three Americans have been among those killed by drones, all in Yemen. Two were killed in the same Sept. 30, 2011, strike: Al-Awlaki, who was born in New Mexico and who Obama administration officials claim was the operations chief of Al-Qaida's Arabian Peninsula branch, and Samir Khan, an Islamist writer who grew up in New York City and whose family now lives in North Carolina. Al-Awlaki's teenage son, who was born in Colorado, died in a separate drone strike two weeks later.