Yeah, you can do that. There is a special setting in the Options section.
1) No protection. All public pages can be seen by all visitors. This is the default setting
2) Content only. This means that the entire navigation of your blog is publicly visible. However, you decide what is displayed in the navigation. If someone then clicks on an article in a blog navigation a password is requested.
3) Content and navigation. The blog is not visible. Visitors need a link to an article to read it.