WASHINGTON, March 16 (Reuters) - U.S. national security officials are questioning a decision by military prosecutors to allege that Army Private Bradley Manning aided Al Qaeda's Yemen-based affiliate by leaking documents to the WikiLeaks website.

At a procedural hearing on Thursday at Ft. Meade, Maryland in preparation for Manning's court-martial, a military judge said defense lawyers had asked for particulars of a charge that Manning had aided an enemy.

The judge, Colonel Denise Lind, read a document from prosecutors which identified the enemy as "Al Qaeda in the Arabian Peninsula," one of Al Qaeda's most potent affiliates and known in the counter-terrorism world as AQAP.

She added that prosecutors had said Manning indirectly aided this group by providing material to WikiLeaks.

Defense Department spokesmen had no comment on the claims. A spokeswoman for the Military District of Washington, whose prosecutors are pursuing the case against Manning, did not respond to messages requesting comment.

On Friday, Colonel Lind denied requests by Manning's lawyers to interview witnesses who could comment on classification issues and the national security damage of Manning's alleged leaks. A trial is expected later this year.

Manning, 24, faces life in prison if convicted of aiding the enemy, the most serious of 22 charges against him. Other charges include wrongfully causing intelligence to be published on the Internet and theft of public property.

Numerous U.S. defense and security officials contacted by Reuters said they did not know what specific aid Manning's alleged leaks to WikiLeaks provided to AQAP.

Former State Department spokesman P.J. Crowley, who left his position after criticizing Army brass for the harsh confinement regimen imposed on Manning, described the aiding the enemy charge as "unnecessary and an overreach.

"It's a hard case and an unnecessary case to make. ... It undermines the credibility of the prosecution," Crowley said.

Other U.S. officials, all of whom asked for anonymity, said they were unaware of specific benefits to AQAP which had been afforded by leaks of U.S. government files to WikiLeaks.

Three current and one former U.S. national security official said it was possible that militant groups like Al Qaeda could glean information about American counter-terrorism strategy and tactics by poring through hundreds of thousands of U.S. government documents, including field reports from military units in Iraq and Afghanistan, WikiLeaks made public.

But these officials said they had no information about how specific items acquired by WikiLeaks might have aided AQAP.

"The alleged disclosure of classified information, while deplorable, does not in and of itself constitute an act of terrorism," said one current official, who requested anonymity.

AKIN TO ACCUSATION OF TREASON

Civil liberties advocates argued it was inappropriate for prosecutors to have charged Manning with aiding the enemy. The charge could carry the death penalty, although Manning case prosecutors say they will not seek capital punishment.

Ben Wizner, a lawyer for the American Civil Liberties Union, said charges of aiding the enemy have not historically been proffered against suspects not accused of communicating directly with an enemy. He said the charge is akin to an accusation of treason.

"To apply it to this kind of conduct is breathtaking," Wizner said. "It means any time a Pentagon spokesman stands up at the podium he's aiding the enemy.

"What it really means is that any newspaper who publishes these leaks is aiding the enemy," he said. "The logic of the charge suggests that any time any member of the military says anything that might reach Al Qaeda, that member of the military is aiding the enemy.

"I think this is a gross violation of the First Amendment to apply this provision to someone who shared info with the press apparently with the intention of educating the public, not aiding the enemy," Wizner added.

Geoffrey Robertson, a prominent British human rights lawyer who has represented WikiLeaks founder Julian Assange in his extradition fight against questioning in Sweden in a sexual misconduct investigation, said after WikiLeaks started posting secret U.S. government documents in 2010, "it was widely predicted that Julian Assange would have blood on his hands."

To date, however, no deadly or injurious attacks on anyone have been attributed to WikiLeaks publication of official U.S. files, Robertson claimed.

Authorities have been suggesting for months that Manning might have aided a U.S. enemy via WikiLeaks. At last year's preliminary hearing, prosecutor Ashden Fein showed the court a sub-titled video of an al Qaeda recruiter who, citing WikiLeaks, urged followers to "take advantage of the wide range of resources available today on the Internet."

Fein said Manning knew the information he allegedly leaked could be used by enemies like "al Qaeda, al Qaeda in the Arabian Peninsula and classified enemies." Prosecutors alluded to evidence which included an AQAP magazine and a video featuring an English-language spokesman for the group. An issue of AQAP's "Inspire" magazine published in late 2010 quoted Assange.

U.S. diplomatic cables published by WikiLeaks included classified reports of talks between Gen. David Petraeus, then U.S. military commander in the region, and then-Yemen president Ali Abdullah Saleh about counter-terrorism cooperation.

(Reporting by Mark Hosenball and Lily Kuo)

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