thanks for advise.
I tried both ways and even tried another way typical for SUSE:
I have used YaST to configure /etc/sudoers.
In the beginning nothing worked :-( but I have found out what kind of mistake I have done. I tried to use shutdown command as I used to do with root - something like this:
sudo shutdown -h now
It didn't worked. I was always asked for root password, but when I entered:
sudo /sbin/shutdown -h now
everything works as expected.