Tyler Tork

Like blog posts, a Page can have an “Excerpt” field to override the automatic excerpt of 55 words from the beginning of the content. However, many themes don’t display this field when editing pages, so you can’t edit it.
This extremely simple plugin forces page excerpt capability “on”. The Page excerpt is visible in internal search results and “Query Loop” blocks, as well as in the output of many plugins (e.g. CC Child Pages). So I generally do want to decide for myself whether to accept the default excerpt.

Torknado Page Excerpt

Pages, like Posts, can have an Excerpt field to override the automatic "first 55 words" excerpt. However, many themes don't enable edit …

Andrew Ozz

Excerpt Editor provides a convenient place for creating and editing all excerpts. It can also add custom excerpts for pages (not possible without a plugin). Features: auto-creating excerpts when publishing new Posts and Pages, displaying customisable excerpts from the content for posts without an excerpt, appending excerpts from the latest posts to each Post or from the sub-pages to each Page, replacing the content for all archive and tags pages with excerpts (eliminates content duplication for SEO).
The excerpts can be used in the RSS feed, displayed on the Home or Archive pages and/or used for meta descriptions. The excerpts can be in any language supported by WordPress and the plugin contains .pot file to facilitate translations.

Excerpt Editor

Quick edit or create excerpts for both Posts and Pages, auto-generate and append excerpts or replace the content with excerpts.

Torknado Page Excerpt vs Excerpt Editor