I have tried emerging kde 3.0.2 without qt3. Emerge ought to know that KDE depends on qt3. It seems a dependency is missing.
Please give some more details: the profile you're using (where the /etc/make.profile symlink is pointing), version of emerge, and an example of this happening - the output of 'emerge kde -pe' not containing qt, for instance.
Seems to be fixed in 3.0.3