Sorry but that made absolutely no sense to me. What is alt-n suppose to be?
What you could try is use control-alt-f1 to switch to one of the other virtual consoles, that doesn't log you off but it will place you on the console.
However, if you want the login manager (file]kdm[/file]? or... what?) to be able to perform tasks such as shutting down the system then if I'm not mistaken that requires you to change a few settings in order to give them the permissions to do so. I don't know from mind what, but I assume it also depends on the login manager you're using (if any).
So: if this about logging off from inside KDE or the login manager? And if this is the login manager; which one are you using?