Pablo Martinez Monsivais/Associated Press

John O. Brennan, President Obama’s choice to be director of the C.I.A., has been the president’s counterterrorism adviser.

The White House announcement appears to refer to a long, detailed 2010 memo from the Justice Department’s Office of Legal Counsel justifying the killing of Anwar al-Awlaki, an American-born cleric who had joined Al Qaeda in Yemen. He was killed in a C.I.A. drone strike in September 2011. Members of Congress have long demanded access to the legal memorandum.

The decision to release the legal memo to the Intelligence Committees came under pressure, two days after a bipartisan group of 11 senators joined a growing chorus asking for more information about the legal justification for targeted killings, especially of Americans.

The announcement also came on the eve of the confirmation hearing scheduled for Thursday afternoon for John O. Brennan, President Obama’s choice to be director of the C.I.A., who has been the chief architect of the drone program as Mr. Obama’s counterterrorism adviser.

Critics accused Mr. Obama of hypocrisy for keeping the legal opinions on targeted killing secret, noting that in 2009 he had ordered the public release of the classified memos governing C.I.A. interrogations under President George W. Bush. Administration officials replied that the so-called enhanced interrogations had been stopped, while drone strikes continue.

Until Wednesday, the administration had refused to even officially acknowledge the existence of the documents, which have been reported about in the press. This week, NBC News obtained an unclassified, shorter “white paper” that detailed some of the legal analysis about killing a citizen and was apparently derived from the classified Awlaki memorandum. The paper said the United States could target a citizen if he was a senior operational leader of Al Qaeda involved in plots against the country and if his capture was not feasible.

Administration officials said Mr. Obama had decided to take the action, which they described as extraordinary, out of a desire to involve Congress in the development of the legal framework for targeting specific people to be killed in the war against Al Qaeda. Aides noted that Mr. Obama had made a pledge to do that during an appearance on “The Daily Show” last year.

“Today, as part of the president’s ongoing commitment to consult with Congress on national security matters, the president directed the Department of Justice to provide the Congressional Intelligence Committees access to classified Office of Legal Counsel advice related to the subject of the Department of Justice white paper,” said an administration official who requested anonymity to discuss the handling of classified material.

The official said members of the Intelligence Committees would now get “access” to the documents.

Christopher Anders, senior legislative counsel for the American Civil Liberties Union, called the president’s move “a small step in the right direction.” But he noted that the legal memo or memos were not being shared with the Armed Services Committees, which have jurisdiction over Pentagon strikes, or the Judiciary Committees, which oversee the Justice Department. It was not clear whether the release involved more than one memo.

The public should be permitted to see at least a redacted version of the relevant material, Mr. Anders said. “Everyone has a right to know when the government believes it can kill Americans and others,” he said.

The Senate Intelligence Committee is expected to closely question Mr. Brennan about his role in the drone program during his hearing. Senator Ron Wyden, an Oregon Democrat who sits on the committee, said in a phone interview that he had been working in his office on questions for Mr. Brennan about 6:30 p.m. Wednesday when Mr. Obama called him and said that “effective immediately he was going to make the legal opinions available and he also hoped that there could be a broader conversation.”

Mr. Wyden has repeatedly called on the administration to release its legal memorandums laying out what the executive branch believes it has the power to do in national security matters, including the targeted killing of a citizen. Earlier on Wednesday, at a Democratic retreat in Annapolis, Md., he had hinted at a potential filibuster of Mr. Brennan’s nomination by vowing to “pull out all the stops to get the actual legal analysis, because without it, in effect, the administration is, in effect, practicing secret law.”

Mr. Wyden said that committee members would have immediate access to the material, and that there would be a process for other senators to read it eventually. It was not clear whether lawmakers’ legal aides would also be allowed to read it.

He said the administration’s decision to allow lawmakers “to finally see the legal opinions” was an “encouraging first step, and what I want to see is a bipartisan effort to build on it, particularly right now, when the lines are blurring between intelligence agencies and the military.”

The Congressional Intelligence Committees were created in the late 1970s to exercise oversight after a series of scandals at the spy agencies. The law requires that the committees be kept informed of intelligence activities. But most administrations withhold at least some legal opinions, treating them as confidential legal advice to the president and agency officials.

Senator Dianne Feinstein, the California Democrat who leads the Senate Intelligence Committee, said she was pleased by the president’s action. “It is critical for the committee’s oversight function to fully understand the legal basis for all intelligence and counterterrorism operations,” she said.

The New York Times and the American Civil Liberties Union have filed lawsuits to force the release of the classified legal opinions on targeted killing, including the one now going to the Intelligence Committees. A judge rejected the claims, and the decision is on appeal.

The use of unmanned drones in the war against terrorism — a technology that has greatly facilitated the ability of the government to kill specific people far from any “hot” battlefield — has significantly escalated under Mr. Obama, who has used them to target Qaeda leadership. Mr. Obama has hailed his administration’s success in killing many in the terrorist organization’s senior ranks and undermining its ability to attack America.

But there have been persistent questions about how targets are chosen, especially when it comes to American citizens who the government says have taken up arms against their country as part of Al Qaeda or other terrorist organizations.

Mr. Obama and administration officials have said they are pursuing a “legal framework” for those decisions, and some top officials have given speeches describing that legal framework. The unclassified white paper had been provided to members of Congress but had not been released publicly.

Jay Carney, the White House press secretary, was asked on Wednesday morning whether the president owed the public a “clearer explanation” about the standards that the government must meet before it uses the drones to kill Americans overseas. He called that an “excellent question” and said Mr. Obama took it seriously.

“He’s talking about this in a very deliberative and thoughtful way about how we move forward as a nation on these issues, because, obviously, 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,” Mr. Carney said.

Asked about the timing of those deliberations, he said he did not have any information to provide. “But I just wanted to convey to you the seriousness with which the president approaches these issues, and he respects the questions being asked,” Mr. Carney said.