Tnx for the answer. 
Yes I can see in my browser www.site.com/dir2 because the directory listing is
allowed but httrack download all files in this directory only if I specify in
the url.txt www.site.com/dir2. 
If I simply run httrack www.site.com -parameters (without -%L urls.txt) it
doesn't try to download files *not linked in any pages* but visible and
accessible pointing the browser to the directory.

An example: www.site.com have some html pages that links the page
www.site.com/dir1/subdir1/subsubdir1/page.html. 
Httrack download this page but doesn't look for files in
www.site.com/dir1/subdir1/subsubdir1/, www.site.com/dir1/subdir1/ and
www.site.com/dir1/. 

P.S. I'm using httrack 3.42