FORT MEADE, Md. — The prosecution is poised to begin laying out its case against the young soldier blamed for the largest leak of classified material in American history after an Army appeals court late Friday rejected a defense effort to remove the presiding officer.

The long-awaited military court case against Army Pfc. Bradley Manning, the accused source for the WikiLeaks website’s trove of U.S. military and diplomatic secrets, will go forward with Lt. Col. Paul Almanza as the presiding officer. The defense requested that Almanza, an Army Reserve lieutenant colonel and Justice Department prosecutor, step aside because of alleged bias.

Almanza rejected the request and refused to suspend the hearing pending an appeal.

Manning, a one-time intelligence analyst stationed in Baghdad, is accused of leaking hundreds of thousands of sensitive items including Iraq and Afghanistan war logs, and State Department cables.

The Obama administration says the released information has threatened valuable military and diplomatic sources and strained America’s relations with other governments.

Friday was Manning’s first appearance in public after 19 months in detention.