Oracle 调度器DBMS_SCHEDULER调用alter语句执行失败？

[zlc409057173]

begin
    DBMS_SCHEDULER.CREATE_SCHEDULE (
      schedule_name     => 'BPH_START_TRACE_SCHEDULE',
      start_date        => to_date(to_char(sysdate,'yyyy-MM-dd') || ' 15:00:00','yyyy-MM-dd hh24:mi:ss'),
      repeat_interval   => 'FREQ=DAILY;INTERVAL=1',
      comments          => 'every one day 10 PM start trace');
END;
/
BEGIN
    DBMS_SCHEDULER.CREATE_PROGRAM (
        program_name           => 'BPH_START_TRACE_PROGEAM',
        program_action         => 'begin 
                                      EXECUTE IMMEDIATE alter system set sql_trace=true; 
                                    end ',
        program_type           => 'PLSQL_BLOCK',
        enabled                => TRUE);
END;
/
BEGIN
    DBMS_SCHEDULER.CREATE_JOB (
        job_name           =>  'BPH_START_TRACE_JOB',
        program_name       =>  'BPH_START_TRACE_PROGEAM',
        schedule_name      =>  'BPH_START_TRACE_SCHEDULE',
        enabled            =>  true);
END;
/

为什么上面的执行报异常，JOB执行不成功？
下面是异常信息

ORA-06550: 第 2 行, 第 57 列: 
PLS-00103: 出现符号 "ALTER"在需要下列之一时：
 ( - + case
   mod new not null <an identifier>
   <a double-quoted delimited-identifier> <a bind variable>
   continue avg count current exists max min prior sql stddev
   sum variance execute forall merge time timestamp interval
   date <a string literal with character set specification>
   <a number> <a single-quoted SQL string> pipe
   <一个带有字符集说明的可带引号的字符串文字>
   <一个可带引号的 SQL 字符串> purge

[zlc409057173]

请大佬帮忙指点