The Army ordered a general court-martial on a charge of desertion for a private who defected to the Soviet Union and then changed his mind and returned to the West. The order by Ft. Dix commander Maj. Gen. Rocco Negris overruled a recommendation for a lower-level prosecution made by an Army investigator who held a hearing last week into the case of Pvt. Wade E. Roberts. Ronald Kuby, Roberts' civilian defense counsel, accused the Army of treating Roberts far more harshly than most soldiers who go absent without leave because he fled to the Soviet Union rather than to a non-Communist country. Roberts, 22, of Apple Valley, Calif., is being held in a military brig in Philadelphia. The combat wireman left his base in West Germany in March and traveled to the Soviet Union with his West German girlfriend.