Hi,
This is how you should switch from any local google website to google.com
1. lets test, browse google.com
2. you'll be redirect to your local google site, on the footer you'll see a link with google.com. click that link.
3. if this is what you expect to get as default then all you got to do is just browse this url:
http://www.google.com/ncr = google.com
and you are good to go.
good luck
Bentzy.