Restricting Postgres

Is there a way to restrict how much load a PostgreSQL server can take
before dropping queries in order to safeguard the server? I was
looking at the login.conf (5) man page and while it allows me to limit
by processor time this seems to not fit my specific needs.

Essentially, I am looking for a sort of functionality similar to what
Sendmail and Apache have. Once the load of the system reaches a
certain defined limit the daemon drops tasks until such a time that it
can resume normal operation.

While not necessarily common on my servers I have witnessed some fairly
high load averages which may have led to the machine dropping outright.
Any help on this matter would be appreciated.
--
Martin Foster
Creator/Designer Ethereal Realms
martin(at)ethereal-realms(dot)org