С www на без www, 2 вариант наоборот.
AddDefaultCharset UTF-8
RewriteEngine on
RewriteCond %{HTTP_HOST} ^www.site\.ru$ [NC]
RewriteRule ^(.*)$
http://site.ru/$1 [R=301,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?%{QUERY_STRING} [L]
#<IfModule mod_security.c>
#SecFilterEngine Off
#SecFilterScanPOST Off
#</IfModule>
#<IfModule security_module>
#SecFilterEngine Off
#SecFilterScanPOST Off
#</IfModule>
#<IfModule security2_module>
#SecFilterEngine Off
#SecFilterScanPOST Off
#</IfModule>
AddDefaultCharset UTF-8
RewriteEngine on
RewriteCond %{HTTP_HOST} ^site\.ru$ [NC]
RewriteRule ^(.*)$
http://www.site.ru/$1 [R=301,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?%{QUERY_STRING} [L]
#<IfModule mod_security.c>
#SecFilterEngine Off
#SecFilterScanPOST Off
#</IfModule>
#<IfModule security_module>
#SecFilterEngine Off
#SecFilterScanPOST Off
#</IfModule>
#<IfModule security2_module>
#SecFilterEngine Off
#SecFilterScanPOST Off
#</IfModule>