I had the same issue as the original poster. I want EasyPG to save files with a .asc extension in ASCII-armored ciphertext, not binary. There's some good info in the responses, but none was complete enough to solve the OP's issue. I think I solved it with the following configuration.
(setq epa-file-name-regexp "\\.\\(gpg\\|\\asc\\)\\(~\\|\\.~[0-9]+~\\)?\\'")
;; Minor mode for ASCII-armored gpg-encrypted files
"Save files in encrypted, ASCII-armored format"
;; The initial value.
;; The indicator for the mode line.
;; The minor mode bindings.
(if (symbol-value auto-encryption-armored-mode)
(set (make-local-variable 'epa-armor) t)
(add-to-list 'auto-mode-alist '("\\.asc$" . auto-encryption-armored-mode))
First, this adds .asc and Emacs backup names to the file name extensions that EasyPG will save as encrypted data, by default binary.
Then it defines a minor mode that sets epa-armor as a buffer local variable. Inspired by sensitive-mode: http://anirudhsasikumar.net/blog/2005.01.21.html
Finally, it sets that minor mode to automatically activate when opening .asc files. TODO: Also activate when opening Emacs backup files.
Note that the "extra" epa-file-name-regexp regexp syntax is critical if you don't want cleartext copies of your .gpg and .asc files floating around as Emacs backups.
Seems to work OK so far.
This question is pretty stale, but there's also not an easy solution shipped with EasyPG and Emacs 24 on Debian 8.3. Hope that helps.