WASHINGTON — President Obama on Friday moved to cement his administration’s historic opening with Cuba by issuing a sweeping directive that will last beyond his presidency, setting forth a new United States policy to lift the Cold War trade embargo and end a half-century of clandestine plotting against Cuba’s government.

The action formalizes the shift toward normalization that the president unveiled nearly two years ago with the announcement that he and President Raúl Castro of Cuba had secretly agreed to repair their countries’ relationship.

Mr. Obama on Friday also made what aides said were likely his final major modifications to loosen United States sanctions on Cuba before leaving office, including lifting the $100 limit on bringing Cuban rum and cigars into the United States.

It is Mr. Obama’s latest use of executive power to press forward in the face of lingering opposition in Congress to repealing the embargo, this time through a 12-page document that essentially transforms what has been a presidential priority into a set of official mandates that will shape United States policy toward Cuba for decades.