SET serveroutput on
SET lines 100
DECLARE
   h1 NUMBER;
BEGIN
  -- Format: DBMS_DATAPUMP.ATTACH('[job_name]','[owner_name]');
   h1 := DBMS_DATAPUMP.ATTACH('IMPORT_USER000323','SYSTEM');
   DBMS_DATAPUMP.STOP_JOB (h1,1,0);
END;
/