Why doesn't the site work with "www"?

Question

Apache HTTP Server

site.ru - everything is fine.
www.site.ru - redirects to the main hosting page.
Decided to redirect. Here is my .htaccess file:

AddDefaultCharset utf-8

DirectoryIndex index.php

RewriteEngine On
RewriteCond %{HTTP_HOST} ^www\.(.*)$
RewriteRule ^(.*)$ http://%1/$1 [L,R=301]

But doesn't work.
What's wrong?