“Today’s announcement will only serve to tighten the noose the Castro regime continues to have around the neck of its own people,” Senator Robert Menendez, Democrat of New Jersey, said in a statement. He said Congress had not been consulted on the move, and he added, “The Obama administration seeks to pursue engagement with the Castro regime at the cost of ignoring the present state of torture and oppression, and its systematic curtailment of freedom.”

Benjamin J. Rhodes, the deputy national security adviser, who led clandestine negotiations that produced the 2014 opening, said most Cubans who came to the United States in the past “absolutely had to leave” Cuba “for political purposes.” Now, he said, the flow is largely of people seeking greater economic opportunity. Ending the policy, he added, is a reflection of Mr. Obama’s view that, ultimately, the rise of a new generation of Cubans pressing for change in their own country is vital to bringing about change there.

“It’s important that Cuba continue to have a young, dynamic population that are agents of change,” Mr. Rhodes said.

Jorge Mas, the chairman of the Cuban American National Foundation, said the changes would force Cuba’s leaders to be more responsive to their citizens. “People may be initially upset at not being able to have this way of getting out of Cuba, but ultimately, the solution for Cuba is people fighting for change in Cuba,” Mr. Mas said.

The change in policy essentially guts the Cuban Adjustment Act of 1966, which assumed that Cubans were political refugees who needed protection and allowed those who remained in the United States for more than a year to become legal residents.

Obama administration officials urged Congress on Thursday to repeal the measure, but in the interim, by eliminating the policy that automatically afforded parole to Cubans arriving in the United States, they have essentially denied Cuban migrants the opportunity to take advantage of its benefits.

Cuba, likewise, still has a law in place that denies re-entry to migrants once they have been gone for four years or more; Mr. Rhodes said officials in Havana have pledged to repeal it once the United States Congress scraps the Cuban Adjustment Act.