/sys$common/syshlp/helplib.hlb SET, QUEUE, Qualifiers, /BASE_PRIORITY  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /BASE_PRIORITY=n

    Specifies the base process priority at which jobs are initiated
    from a batch execution queue. The base priority specifier can be
    any decimal value from 0 to 15.

    You also can specify this qualifier for an output execution
    queue. In this context the /BASE_PRIORITY qualifier establishes
    the base priority of the symbiont process when the symbiont
    process is created.