The plan envisages greater co-ordination in areas like EU-led peacekeeping missions outside the bloc.
However, EU foreign policy chief Federica Mogherini stressed that the bloc did not intend to compete with Nato or create a European army.
She added that the plan was under consideration before Donald Trump's victory in US presidential elections.
During the campaign, Mr Trump suggested that Washington may not automatically come to the aid of a Nato ally under attack, criticising low levels of defence spending by some EU members of the military alliance.