pg_hba.conf multiple auth_metods question

[Gémes Géza <geza(at)kzsdabas(dot)sulinet(dot)hu>]

Hi,

I have successfully deployed krb5 or pam (with pam_krb5) authentication 
with my clients.
My question is: Can I use both in a failover fashion?
What I try to achieve: Users having kerberos tickets get authenticated 
with the krb5 auth_metod, if they don't have the right ticket they get 
prompted for their password, and get authenticated using pam.
The relevant part of my pg_hba.conf:
host    all         all         10.0.0.0/8          krb5
host    all         all         10.0.0.0/8          pam postgresql

What shall I change to have it working as expected. Currently only the 
first line works (whatever I would put first).

Many thanks for your time and patience.

Geza