No, but it sounds like that might make a useful plugin if someone would code it.

Add in the mod/blog/views/default/blog/listing.php after Line 21 the following code:

$info .= "<p class=\"owner_timestamp\">" . substr(elgg_echo($vars['entity']->description),0,200) . "...<a href=\"" . $vars['entity']->getUrl() . "\">read more »</a></p>";

So 200 is the number of the characters.

Have fun