Can't use rsh as root

["David Gaudine" <david@annette.concordia.ca>]

I'm trying to use rsync from one Debian system to another.
It works fine for transferring files from my user directory
one one system to my user directory on the other,
while I'm logged in to my user account.  When I su to root
and try, I get "permission denied".  auth.log shows

Mar 19 13:02:19 frankie rshd[779]: rsh denied to root@annette as root:
   cmd='rsync --server -vunlWogDtpr --delete --force . /backupa1';
Permission denied.

/root/.rhosts on each system names the other system.
So does /etc/hosts.equiv
I'm copying from a hamm system to a slink system.