Using the_excerpt() on a page

While this was far from clear in the OP at first, I think this might be a good solution. Just make a shortcode to place the excerpt in the body. (This is a bad idea if you want this on every page. This is a good idea if you want it once in a while on some pages in the body.)

Here’s code to put in your functions.php:

function the_excerpt_shortcode() {
    return get_the_excerpt();
}
add_shortcode( 'the_excerpt', 'the_excerpt_shortcode' );

Once you have the, just put this in your page body:

[the_excerpt]

And you’re good to go.

If you’re using Twenty Ten, Twenty Eleven, or some other theme that hooks to the excerpt_more filter, you may have to modify that short code to strip an auto-generated “Continue Reading…” link, but for many themes that’s unnecessary. Consider this a starting point.