WASHINGTON (Reuters) - WikiLeaks founder Julian Assange is expected to plead guilty this week to violating U.S. espionage law, in a deal that could end his imprisonment in Britain and allow him to return home to Australia.

U.S. prosecutors filed criminal paperwork against Assange, 52, that is typically a preliminary step before a plea deal. It outlines a single criminal count of conspiring to obtain and disclose classified U.S. national defense documents, according to filings in the U.S. District Court for the Northern Mariana Islands.

(Reporting by Sarah N. Lynch in Washington; Additional reporting by Michael Holden and Kate Holton in London; Editing by Scott Malone and Matthew Lewis)