g77 doesn't support pointers or allocatable objects
(other than automatic arrays).
This set of features is
probably considered just behind intrinsics
PARAMETER statements on the list of large,
important things to add to g77.
In the meantime, consider using the
declaration to specify that a variable must be
able to hold a pointer.
This construct is not portable to other non-GNU compilers,
but it is portable to all machines GNU Fortran supports
when g77 is used.
See Functions and Subroutines, for information on
constructs, which are useful for passing pointers to
procedures written in languages other than Fortran.