Intentá con
Código Apache:
Ver originalRewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteCond %{HTTP_HOST} !\.([a-z-]+\.[a-z]{2,6})$ [NC]
RewriteRule ^ http://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
Para www a no-www
Código Apache:
Ver originalRewriteCond %{HTTP_HOST} ^www\.(.+)$ [NC]
RewriteCond %{HTTP_HOST} !\.([a-z-]+\.[a-z]{2,6})$ [NC]
RewriteRule ^ http://%1%{REQUEST_URI} [L,R=301]
Saludos