WASHINGTON — Dozens of secret documents justifying the Bush administration's spying and interrogation programs could see the light of day because of a new presidential directive.

The American Civil Liberties Union asked the Obama administration on Wednesday to release Justice Department memos that provided the legal underpinning for harsh interrogations, eavesdropping and secret prisons.

For years, the Bush administration refused to release them, citing national security, attorney-client privilege and the need to protect the government's deliberative process.

The ACLU's request, however, comes after President Barack Obama last week rescinded a 2001 Justice Department memo that gave agencies broad legal cover to reject public disclosure requests. Obama also urged agencies to be more transparent when deciding what documents to release under the Freedom of Information Act.

The ACLU now sees a new opening.

"The president has made a very visible and clear commitment to transparency," said Jameel Jaffer, the director of the ACLU's National Security Project. "We're eager to see that put into practice."

The collection of memos, written by the Justice Department's Office of Legal Counsel, are viewed as the missing puzzle pieces that could help explain the Bush administration's antiterrorism policies.

Critics of the prior administration also see the release of the documents as necessary to determine whether former administration officials should be held accountable for legal opinions that justified various antiterrorism measures, including the use of waterboarding, an interrogation technique that simulates drowning.

Attorney General nominee Eric Holder recently denounced waterboarding as torture, but details about how the method was used have remained secret.

"We don't have anything resembling a full picture of what happened over the last eight years and on what grounds the Bush administration believed it could order such methods," Jaffer said. "We think the OLC memos are really central to that narrative."

Even though some key memos have been released or leaked to the media, at least 50 memos remain secret, Jaffer said, including a dozen memos related to the warrantless wiretapping program.

In one case, the ACLU found out about a memo because it was cited in a footnote. The government has refused to elaborate on the 2002 document, other than to describe it as a discussion of the Fourth Amendment's application to domestic military operations.

Jaffer said that it could reveal whether the Justice Department was advising the National Security Agency that the Fourth Amendment didn't apply to its eavesdropping program, but he's not certain. The amendment guards against unreasonable search and seizure.

"There are about a dozen memos where we just have one or two lines about the subject matter and that's it," he said. "When you put it all together you realize how much is still being held secret."

The ACLU originally sought the documents by filing a series of lawsuits under FOIA.

Federal judges have ordered the release of some records, including thousands of pages documenting the FBI's concerns about the interrogation program.

The Bush administration, however, fought the release of most of the records.

In September 2007, U.S. District Judge Henry Kennedy rejected the government's claim of secrecy and ordered the Justice Department to submit surveillance documents for his review.

The ACLU has asked another judge to find CIA officials in contempt after revelations that videotapes of CIA interrogations had been destroyed. A criminal investigation is ongoing.

Since Obama's directive on disclosure, Melanie Ann Pustay, the director of Justice's Office of Information and Privacy, instructed federal officials that they should process requests for records with a "clear presumption in favor of disclosure, to resolve doubts in favor of openness, and to not withhold information based on 'speculative or abstract fears.'"

In another indication that the ACLU may get its way, the nominee to head the OLC, Dawn Johnsen, has previously indicated she thinks that such memos should generally be released.

Before her nomination, Johnsen wrote in an article for Slate, the internet magazine, that the central question in the debate was whether OLC could issue "binding legal opinions that in essence tell the president and the executive branch that they need not comply with existing laws — and then not share those opinions and that legal reasoning with Congress or the American people? I would submit that clearly the answer to that question must be no."