VMS Help FORTRAN, Intrinsic Procedures, IARGPTR  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  IARGPTR ()

  A function that returns a pointer to the actual argument list for
  the current routine.  The result is an INTEGER*4 data type.  The
  actual argument list is an array of INTEGER*4 values, the first of
  which contains the argument count.