problem with “www”

hello

i have wordpress 2.9

i want my site open with both (www.myurl.com and myurl.com)

in a managment menu , i entry “myurl.com” in a urlbox
and then i write this code in htaccess

RewriteCond %{HTTP_HOST} !^myurl.com$ [NC]
RewriteRule ^(.*)$ https://myurl.com/$1 [R=301,L]

know my site opening with both(www.myurl.com and myurl.com)
but admin page (wp-admin) isnt openning.

for solving this problem i wrote myurl.com in adminurl box, but this isnt work.

sorry my english is not good and my wp is persian