Obama on Monday stated this while backing the position taken by British Prime Minister David Cameron.
"I think the UK's participation in the EU [European Union] is an expression of its influence and its … role in the world," Obama said during a news conference with Cameron, who was visiting the White House.
Cameron is trying to unite his party on the issue after two Cabinet ministers suggested they would vote to leave the EU if a referendum were held on Monday.
Obama said the decision was ultimately up to the people of the UK, and noted there were "tough negotiations" ahead on economic and political issues.
"I will say this, that David's basic point that you probably want to see if you can fix what's broken in a very important relationship before you break it off makes some sense to me," Obama said.
Cameron told reporters that it is in the "national interests of Britain" to work with the EU on reforms that would make it "more open, more competitive, more flexible", and that it made sense to wait until reforms are made to hold a referendum on whether to stay in the EU.
"There's a very good reason why there's not going to be a referendum tomorrow," Cameron said.
"It would be a false choice between the status quo and leaving," he said. – Reuters