Is the login information for Facebook encrypted?

If you look for the lock on the login page, you won't see it, because the login page itself is not encrypted. However, if you look at the HTML code for the page, you will see that the login form posts to:

https://login.facebook.com/login.php

Which means that whatever you enter into that form will be encrypted.

This isn't 100% secure. If the main page is not https, you can't be guaranteed that the information on the page is actually coming from the facebook site. In theory, a man in the middle, or someone who fools your computer into thinking www.facebook.com is on another site, could supply a different form that doesn't post to the encrypted site on facebook.com.

In practice, though, I'd be surprised if anyone tried that sort of attack on facebook... A banking site would be a more likely target.

check the address field for https and check to see if there is a lock on the status bar of your browser

Yes it is.