WASHINGTON — In a major reversal, the Obama administration said Tuesday it will not allow oil drilling in the Atlantic Ocean.

Interior Secretary Sally Jewell made the announcement on Twitter, declaring that the administration’s next five-year offshore drilling plan “protects the Atlantic for future generations.”

A formal announcement is expected later in the day.

The decision to block Atlantic drilling reverses a proposal made last year in which the administration floated a plan that would have opened up a broad swath of the Atlantic Coast to drilling. The January 2015 proposal would have opened up sites more than 50 miles off Virginia, North and South Carolina and Georgia to oil drilling no earlier than 2021.

The Interior Department said the latest decision responds to strong local opposition and conflicts with competing commercial and military ocean uses.

The Pentagon said Atlantic offshore drilling could hurt military maneuvers and interfere with missile tests the Navy relies on to protect the East Coast.

Environmental groups also opposed Atlantic drilling and had organized protests and petitions in affected states.

“President Obama has taken a giant step for our oceans, for coastal economies and for mitigating climate change,” said Jacqueline Savitz, vice president of Oceana, an environmental group. “This is a victory for people over politics and shows the importance of old-fashioned grassroots organizing.”