The White House announced plans last summer to hold both summits back-to-back in Chicago, giving the president a high-profile opportunity to tout his foreign policy and diplomatic credentials on his home turf in an election year.
The idea of moving the G-8 to Camp David was raised to the president a few weeks ago, a senior administration official said, adding that the president was intrigued by the novelty of the idea and asked staff whether they could pull off the change.
The official spoke on condition of anonymity to discuss internal White House thinking.
Adding to the curious nature of the White House announcement was that Obama rarely spends time at his presidential retreat. Unlike many of his predecessors, Obama never has hosted a world leader at Camp David.
Monday's announcement appeared to catch many in Chicago by surprise.
A spokeswoman for Emanuel said the Chicago mayor was informed about the location change in a Monday phone call from a White House official.
The world's eight largest economies are represented in the G-8 and hosting duties for the annual summit are rotated among the member countries. The summits have become targets for large, and sometimes violent, protests in recent years, making security costs a concern for host cities.
At least one protest group heralded the news as a major victory. But Joe Iosbaker of the United National Antiwar Committee in Chicago said protests would still go on during the NATO summit.
Chicago officials began planning for the summits last summer, with city officials predicting it would give the city a chance to shine internationally, while the police rank-and-file worried whether they would be prepared to handle the thousands of protesters expected to converge downtown.