Since I don’t think the_excerpt is going to give you exactly what you want, I would create a custom field called ‘description’. What the code below does is check to see if that field has been filled in, if it has it will display it.
The query at the top of the page makes sure that it is only looping through pages. If you want it to loop through specific sections you’ll need to dig a little deeper into the query.
< ?php query_posts('post_type=page'); ?>
< ?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>