WASHINGTON — Hoping to head off another confirmation battle, the White House said Tuesday that it will allow senators to review a secret paper justifying the drone strike on an American citizen written by one of President Barack Obama's appellate court nominees.

The White House is hoping the memo's disclosure will lead to confirmation of David Barron for the 1st U.S. Circuit Court of Appeals in Boston. Barron is a Harvard Law professor who had worked as acting assistant attorney general at the Justice Department on the case of Anwar al-Awlaki, the American-born al-Qaida leader killed by a U.S. drone in 2011.

Some legal scholars and human rights activists argue it was illegal for the U.S. to kill American citizens away from the battlefield without a trial.

The American Civil Liberties Union wrote a letter to senators on Monday, urging them to delay Barron's confirmation vote until all senators review memos he wrote on the drone program. Republican Sen. Rand Paul of Kentucky also is trying to block Barron's confirmation, barring public release of a redacted version al-Awlaki memo, by virtue of a court order.

Paul last year held up the nomination of CIA Director John Brennan until the administration agreed to release more information about its drone policy. And other Obama nominees, including the president's picks for surgeon general and chief civil rights attorney, have failed to win confirmation this year in the Democratic-controlled Senate amid controversy raised by interest groups.

In Barron's case, the White House quickly responded to the ACLU by offering to show senators an unredacted copy of the 41-page memo he authored July 16, 2010, which argues that targeted killing of an American citizen overseas does not violate the Constitution.

White House spokesman Eric Schultz noted that members of the Senate Judiciary Committee, which advanced Barron's nomination on a party-line vote, already had access to the memo. Schultz expressed confidence that Barron would be confirmed and "bring outstanding credentials, legal expertise and dedication to the rule of law to the federal bench."

"The administration is working to ensure that any remaining questions members of the Senate have about Barron's legal work at the Department of Justice are addressed, including making available in a classified setting a copy of the al-Awlaki opinion to any senator who wishes to review it prior to Barron's confirmation vote," Schultz said.

The 2nd U.S. Circuit Court of Appeals in New York ruled last month that the Obama administration must publicly disclose a redacted version of the memo. The administration is considering whether to appeal the ruling.

Chris Anders, the ACLU's senior legislative counsel, said Barron reportedly signed at least two memos on the drone program and that all his opinions should be revealed to senators, not just the one. "This is short-changing senators who should be getting information that they need to review before voting on a lifetime appointment," Anders said.

At least one Democrat, Sen. Mark Udall of Colorado, said he won't support Barron unless the White House complies with the court order to publicly disclose a redacted version of Barron's memo. "David Barron is highly qualified, but as one of the authors of the Anwar al-Awlaki opinion, Barron's nomination understandably raises key questions about the administration's legal justification for the targeted killing of Americans and about its year-old pledge of greater transparency," Udall said in a statement.

Paul also said he would continue to oppose Barron barring public disclosure. "A federal court has ordered the public release of a redacted legal memo authored by Barron and I believe that anything short of that is inadequate," Paul said in response to the White House offer.

Another Democrat, Sen. Ron Wyden of Oregon, also called for the drone memos to be released publicly but isn't yet taking a position on Barron's confirmation. Wyden has reviewed the documents as a member of the Senate Intelligence Committee and says although al-Awlaki's killing was legitimate, the memos "leave many important questions unanswered."

"I have continued to press the executive branch to answer these important questions, and to provide the full details of the government's legal reasoning to the public, so that American voters can debate whether the president's authorities are subject to adequate limits and boundaries," Wyden said in a statement.