the owner of the files will be set to the user that is running the svn command because of how it implements the underlying up command – it removes and replaces files that are updated, which will cause the ownership to ‘change’ to the relevant user. The only way to prevent this is to actually perform the svn up as the user that the files are supposed to be owned as. If you want to ensure that they’re owned by a particular user, then run the command as that user.
With regards to the permissions, svn is only obeying the umask settings of the account – it’s probably something like 066 – in order to ensure that the file is inaccessible to group and other accounts, you need to issue ‘umask 077’ before performing the svn up, this ensures that the files are only accessible to the user account issuing the command.
I’d pay attention to the security issue of deploying the subversion data into the web server unless the .svn directories are secured.