The Justice Department will publicly release a secret 2011 memo that provided the legal justification for the killing of American terrorism suspects overseas, according to a U.S. official, following extensive pressure on the administration to do so.

The department had been weighing whether to appeal a court order to disclose the memo but informed the White House on Tuesday that it would not, the official said. The decision came on the eve of a Senate vote on President Obama’s nomination of David J. Barron, one of the memo’s authors, to a federal appeals court judgeship.

A group of liberal and conservative senators had said they would fight the nomination unless the memo was made public, and others from both parties had called for its release. The White House allowed lawmakers to view copies of the memo last week in a secure Senate room.

The administration acknowledged last year that drones had killed four U.S. citizens in Yemen, including cleric Anwar al-Awlaki, who was targeted by a CIA drone attack in September 2011. Obama called Awlaki the head of foreign operations for al-Qaeda in the Arabian Peninsula.

A federal court ruled this year that the CIA, the Defense Department and the Justice Department did not have to respond to Freedom of Information Act requests for documents related to drone killings in general, and more specifically the targeted killings of U.S. citizens. The U.S. Court of Appeals for the 2nd Circuit overturned that decision April 21.

Speaking at National Defense University, President Obama said the civilian deaths that have resulted from drone strikes haunt him, but “the unspeakable loss” is better than not acting at all. (Sarah Parnass/The Washington Post)

The government had 45 days in which to ask the appeals panel to review the case anew. The administration official, who spoke on the condition of anonymity about the unannounced decision, said it covered all requested information, not just the Awlaki memo.

In addition to a court-approved, redacted version of the memo, the order covered listings of all classified documents — but not the documents themselves — responsive to the original FOIA requests, filed by reporters for the New York Times and the American Civil Liberties Union.

ACLU Deputy Legal Director Jameel Jaffer said they had not been notified of any decision by the Justice Department. “We’d welcome the public release of this document,” he said of the memo. “The government claims authority to carry out targeted killings of Americans deemed to threaten national security — the public surely has a right to know the breadth of the authority the government is claiming as well as the legal basis for it.”

Sen. Ron Wyden (D-Ore.), a critic of the administration’s drone policy, called news of the decision “very constructive.” Wyden, who said he will announce his decision on the Barron vote on Wednesday, said the release is “very much in the public interest.”

When asked about the fate of Barron’s nomination Tuesday, Senate Majority Leader Harry M. Reid (D-Nev.) told reporters, “I think we’ll be okay.”

The White House referred all questions on the Barron memo to the Justice Department, where officials declined to comment.

News of the Justice Department decision — which the administration official said was made last week by Solicitor General Donald B. Verrilli Jr. with the concurrence of Attorney General Eric H. Holder Jr. — was first reported by the Associated Press.

The official said that the redacted memo probably will be released in a “matter of weeks.”

As part of its consideration of the case, the appeals court, after listening to government arguments, made its own redactions to the Barron memo. That is the version that the court has now ordered the administration to release. But the official said that the administration will go back to the court and re-argue for additional redactions on national security grounds.

At issue is likely to be whether the court agrees to redact references to CIA responsibility for the Awlaki strike. Although the administration has acknowledged the strike, it has never said which agency was responsible for it. The Defense Department also has carried out drone strikes in Yemen.

Last week’s White House agreement to allow senators private access to the memo did not sway some lawmakers opposing Barron’s confirmation, who insisted that the administration comply in full with the appeals court ruling.

Obama’s nomination of Barron, a law professor at Harvard University, was approved by the Senate Judiciary Committee on a vote of 10 to 8 in January. While working at the Justice Department’s Office of Legal Council, Barron was the principal author of at least one memo that served as the legal foundation for the drone strike that killed Awlaki.

Last year, Holder sent a letter to the Judiciary Committee outlining the administration’s guidelines for targeting U.S. citizens, saying killing would be used as a last resort when a person posed “an imminent threat of violent attack against the United States” and capture was “not feasible.”

Holder acknowledged the deaths of four U.S. citizens in drone strikes in Yemen, including Awlaki’s 16-year-old son, but said that only Awlaki had been a target. The others were killed incidentally in strikes against other targets.

Outlining his updated drone policy in a speech one year ago, Obama said that he had authorized Holder to reveal that information “to facilitate transparency and debate on this issue and to dismiss some of the more outlandish claims that have been made.”

“For the record,” Obama said, “I do not believe it would be constitutional for the government to target and kill any U.S. citizen — with a drone, or with a shotgun — without due process, nor should any president deploy armed drones over U.S. soil.”

Ed O’Keefe, Julie Tate and Ellen Nakashima contributed to this report.