A key witness in a federal probe into passport information stolen from the State Department was fatally shot in front of a District church, the Metropolitan Police Department said yesterday.Lt. Quarles Harris Jr., 24, who had been cooperating with federal investigators, was found late Thursday night slumped dead inside a car, in front of the Judah House Praise Baptist Church in Northeast, said Cmdr. Michael Anzallo, head of the department's Criminal Investigations Division.