RewriteEngine On
RewriteRule ^(.*).html /xhref.php?xhref_url=$1.html

RewriteRule ^(.*).htm /xhref.php?xhref_url=$1.htm

RewriteCond index.html -f
RewriteRule ^$ /xhref.php?xhref_url=index.html 

RewriteCond index.htm -f
RewriteRule ^$ /xhref.php?xhref_url=index.htm

User-Agent: Yandex
Host: agency.zeta777.com