basically you need to change the default EXCERPT length of your posts.
there are a couple of ways to solve this issue:
- if you aren’t familiar with PHP
Install this plugin at : http://wordpress.org/plugins/advanced-excerpt/
This will allow you to change the the excerpt length from the admin panel.
- if you are familiar with basic PHP
Go to your functions.php in your theme at /wp-content/themes/YOUR_THEME_NAME/functions.php
Add the following code:
function different_excerpt_length($length) {
return 200;
}
add_filter('excerpt_length', 'different_excerpt_length');
You can change 200 to any number you want like 300.
As for showing your summary instead of the full post, you can follow the instructions from wordpress.com like so : http://en.support.wordpress.com/splitting-content/more-tag/
Hope it helps!