WASHINGTON  — President Barack Obama’s campaign said Wednesday it expects the president to become the first incumbent to be outspent by his opponent, outlining the potential for $1 billion in spending from Republican-leaning outside groups supporting Mitt Romney.

Campaign officials said they expected Romney and a collection of Republican-leaning super PACs would spend roughly $1.2 billion to help get him elected against a president who broke all fundraising records in 2008 by hauling in about $750 million. The officials briefed White House and other political reporters only on condition of anonymity in order to discuss internal campaign strategy and polling data.

Romney’s campaign joined with the Republican National Committee to raise more than $76 million in May, outpacing Obama and the Democratic party, which raised a combined $60 million for the month. It was the first time that Obama has been outraised by an opponent since 2007.

Romney campaign spokeswoman Andrea Saul said the Obama campaign is “used to moving the goal posts,” citing projections that Obama’s campaign might raise $1 billion.