In case you'r running a logrotate, which also sets the permissions of the new log files, that might be a good place to make the change. For example, this is a default apache2 logrotate on an Ubuntu server.
andreas@halleck:~$ sudo cat /etc/logrotate.d/apache2
/var/log/apache2/*.log {
weekly
missingok
rotate 52
compress
dateext
delaycompress
notifempty
create 640 root adm
sharedscripts
postrotate
if [ -f "`. /etc/apache2/envvars ; echo ${APACHE_PID_FILE:-/var/run/apache2.pid}`" ]; then
/etc/init.d/apache2 reload > /dev/null
fi
endscript
}
As you see there is a setting called create? Feel free to change it to whatever mode and ownership you want new log files to have. Also, here is how the create option is described in the logrotate(8) man file.
create mode owner group
Immediately
after rotation (before the postrotate
script is run) the log file is created
(with the same name as the log file
just rotated). mode specifies the
mode for the log file in octal (the
same as chmod(2)), owner specifies the
user name who will own the log file,
and group specifies the group the log
file will belong to. Any of the log
file attributes may be omitted, in
which case those attributes for the
new file will use the same values as
the original log file for the omitted
attributes. This option can be
disabled using the nocreate option.