Col. Denise Lind said at a pretrial hearing at Fort Meade, Md., that prosecutors must prove beyond a reasonable doubt Manning had "reason to believe" the hundreds of thousands of files he is accused of delivering to the whistle-blower website could be used to compromise U.S. national security or help a foreign power, The New York Times reported.
The newspaper said prosecutors had argued they should be required to prove only that Manning willfully disclosed defense-related files.
Lind also decided a member of the team that took part in the raid that resulted in the death of Osama bin Laden, presumed to be a Navy SEAL, can testify at Manning's court-martial, The Washington Post reported.
Manning, who has pleaded guilty to some charges, is to be tried in June for leaking the sensitive materials to WikiLeaks.
Prosecutors contend digital media found at bin Laden's compound in Pakistan show the al-Qaida leader had gotten his hands on some of the WikiLeaks material, evidence Manning's actions compromised national security.
Manning's lawyers have maintained the materials are irrelevant to their client's case.