FORT MEADE, Md. — Defense lawyers for Pfc. Bradley Manning asked a military judge on Monday to acquit him of the most serious charge he faces — aiding the enemy by providing classified information to WikiLeaks — as they began to present their witnesses at his court-martial.

Private Manning’s lead lawyer, David E. Coombs, filed four motions asking the judge, Col. Denise R. Lind, to find him not guilty of that charge and several others on the grounds that prosecutors had failed to prove them during their five-week presentation. The judge, who at Private Manning’s request is hearing the case without a jury, did not immediately rule on the matter but asked for a response from the government by Thursday.

Army intelligence analysts who worked with Private Manning in Iraq testified Monday that he stood out for his computer skills and for his deep interest in political and philosophical issues.

“He had a deep belief in news and what was going on, whereas other people were just concerned about going about their day,” one of the analysts, Sgt. David Sadtler, said. He recalled that Private Manning had been upset about a report describing the arrest of several people, either Iraqis or Moroccans, who had been detained by the local authorities for merely printing material critical of the Iraqi government.