WASHINGTON — Before the Senate votes to confirm him as head of the Central Intelligence Agency, John Brennan faces an Oregon senator’s questions on the Obama administration’s use of deadly force.

On Monday, Sen. Ron Wyden, D-Ore., sent a four-page letter to Brennan, seeking information on the administration’s criteria for authorizing the killing of American citizens as part of its counterterrorism efforts.

For years, Wyden has tried — to no avail — to get the intelligence community to divulge the opinions that it says provide the legal basis for its lethal activities.

The situation is unacceptable, Wyden said in the letter.

“For the executive branch to claim that intelligence agencies have the authority to knowingly kill American citizens but refuse to provide Congress with any and all legal opinions that explain the executive branch’s understanding of this authority represents an alarming and indefensible assertion of executive prerogative,” Wyden wrote.

Wyden, a member of the Senate Select Intelligence Committee, said his oath of office obligates him to review these opinions. While he generally announces holds he places on a nomination or legislation, Wyden has given no indication he will single-handedly block Brennan’s nomination.

“It is critically important for Congress and the American public to have full knowledge of how the executive branch understands the limits and boundaries of this authority, so Congress and the public can decide whether this authority has been properly defined, and whether the president’s power to deliberately kill American citizens is subject to appropriate limitations,” the letter continues.

The White House has declined comment on Wyden’s letter.

Brennan, a 25-year CIA veteran who has served as Obama’s homeland security and counterterrorism adviser since 2009, discussed the administration’s use of targeted killings in an April 2012 speech at the Woodrow Wilson International Center for Scholars in Washington, D.C.

The legal basis for “exceedingly rare” lethal drone strikes, including against American citizens, had been delineated in speeches by Attorney General Eric Holder, CIA general counsel Stephen Preston and Jeh Johnson, the former general counsel for the Department of Defense, he said.

“I venture to say that the United States government has never been so open regarding its counterterrorism policies and their legal justification,” Brennan said in his speech.

The decision to authorize a drone strike involves extensive review of the intelligence and does not come easily, he said.

“The president expects us to address all of the tough questions,” he said. “Is capture really not feasible? Is this individual a significant threat to U.S. interests? Is this really the best option? Have we thought through the consequences, especially any unintended ones? Is this really going to help protect our country from further attacks? Is it going to save lives?”

When the target is an American citizen, even more questions must be answered, he said.

In February 2012, in the wake of a September 2011 CIA drone strike in Yemen that killed the American-born cleric Anwar al-Awlaki and magazine editor and publisher Samir Khan, who was an American citizen, Wyden asked Holder for similar information.

The lack of response from the administration is starting to form a pattern of avoiding congressional oversight by simply not responding to congressional requests for information, Wyden said in his letter to Brennan.

“Individual Americans generally do not expect to know every detail about sensitive military and intelligence operations, but voters absolutely have a need and a right to understand the boundaries of what is and is not permitted under the law, so that they can debate what should and should not be legal and ratify or reject decisions that elected officials make on their behalf,” the letter states. “And I believe that every American has the right to know when their government believes it has the right to kill them.”

Senate Intelligence Committee Chairwoman Dianne Feinstein, D-Calif., scheduled Brennan’s confirmation hearing for Feb. 7.