kdesu normal user and root not able to use

[Daud Yunus]

Hi there just installed fresh kubuntu and when I need to access administrator proveleges in kde using my user password or root password does not work
I looked in the sudoers file and my username was not present just the default line and

root ALL =(ALL) ALL

I added 

"username" localhost =(ALL) ALL


now  my user name can access administor priveleges in kde but It does not ask for my password

how can I make is ask to my password ( I would prefer the security)