NEW YORK, Dec 28 (Reuters) - While it may appear that the government's document-leaking case against U.S. Army intelligence analyst Bradley Manning is strong, the defense could have some surprising leverage with prosecutors and force plea negotiations.

Prosecutors may in particular find it difficult to prove the 24-year-old Manning intended to provide the information to enemies of the United States such as al Qaeda, and that the information was helpful to them, legal experts said.

Manning faces 22 charges of participating in the largest leak of classified government documents in history, including the accusation that he had unauthorized possession of information related to national defense and that he stole records belonging to the United States.

At a hearing that concluded last week, military prosecutors presented evidence that Manning downloaded thousands of classified or confidential files that later made their way to the WikiLeaks website. In his closing summation at the hearing, Captain Ashden Fein, the lead prosecutor, said Manning was a well-trained soldier who "used that training to defy our trust."

"He gave the enemies of the United States unfettered access to these documents," Fein said.

Manning's case is being reviewed by investigating officer Lieutenant Colonel Paul Almanza, who will make a recommendation by Jan. 16 on whether or not the military should court-martial Manning.

A court-martial, which could be a few months away, is not much different from a civilian criminal trial. The charges against the accused in a court-martial must be proven beyond a reasonable doubt, just like in civilian court.

The biggest difference is that jurors in a court-martial consist exclusively of members of the military. There were about 1,900 Army courts-martial in fiscal year 2010 and about 60 acquittals, according to U.S. military justice statistics.

If convicted of all counts, Manning would face a maximum punishment of life imprisonment, reduction in rank to the lowest enlisted pay grade, forfeiture of all pay and allowances and a dishonorable discharge, the Army says. The charge of aiding the enemy is a capital offense, but the Army has indicated it will not seek the death penalty.

'SKY IS NOT FALLING'

Although legal observers agree the government's case is a good one, some speculate that prosecutors could have a tough time proving the most serious charge that Manning gave information to the enemy.

During the preliminary hearing, Manning's lawyer, David Coombs, sought to demonstrate that the audience for the leaked information was not foes of the United States, but the American people, and that the country was not put in any danger due to the leaks.

"The sky is not falling, the sky has not fallen and the sky will not fall," said Coombs.

Some military law experts also question whether the government will be able to prove that Manning intended the information to reach militant groups such as al Qaeda. Merely proving that he intended the information to be displayed on the WikiLeaks website may not be enough to convict him of that charge, said some experts.

It could also be difficult for the government to prove that the information was particularly valuable to al Qaeda, said Eugene Fidell, who teaches military law at Yale Law School.

"What is it that he has told al Qaeda indirectly that is of value to al Qaeda? Is everything that is hurtful to the United States in the eyes of the world of value to al Qaeda? I don't think so," Fidell said.

By underscoring those uncertainties, Coombs may have paved the way for a more favorable plea deal, said David Velloney, a military law expert who is a professor at the Regent University School of Law. In the best-case scenario for the defense, Almanza would recommend that Manning not face the charge at a court-martial of giving information to the enemy. Such a recommendation, made to a higher-ranking officer, is not binding. But it could convince the military prosecutors to drop the charge.

"If you can win one battle there and have the government say, 'Nah, that's not such a good idea we go forward on that charge,' then that's a windfall for the defense before the trial begins," Velloney said.

Coombs has signaled he also has some cards to play at any potential sentencing. At a court-martial, there are two stages -- one to determine culpability and the other to determine a sentence. During the sentencing stage, the defense can offer extenuating and mitigating circumstances that would justify a lighter sentence than sought by the government

Throughout the hearing to determine whether a court-martial is appropriate, Coombs attempted to portray Manning as emotionally unstable with gender-identity issues who should not have had access to sensitive government files.

Combs cited emails and memos showing that Manning's superiors were aware of his gender issues and his need for therapy. But no effective action was taken, Coombs argued. The same arguments about Manning's unit could be presented at any potential sentencing.

"They're going to air all the government's dirty laundry," said Velloney. "It potentially softens the government in any plea deal."

(Reporting by Andrew Longstreth)

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