How to make WP sub-blog open showing summary and not full length posts?

I have Reading Settings set to Summary. But on their initial display, all of my WP sub-blogs open by showing all the posts in full length, creating a 30 ft long vertical scroll area.

After the page is open, selecting a Month or a Category properly displays the selections in summary form.

I am using the default 10-20 WP theme.

How can I make the initial display of posts also show only summaries?