Authorise root as postgres

Hi,

Hope this simple question has a simple solution:
How can I authorise root the same previliage as postgres?

My postgres is password protected, I want to use 'psql -U postgres' as a
root without specifying password every time, or for a certain group of
users. How can I do that? I've been banning my head on the walls in
finding a way to achieve it. Still can't find a way to do it with
indent, md5 or even passwords authentication. Please help.

Thanks a lot!

Tong