When rebels want to return to Syria to fight, Jordan’s intelligence services give them specific times to cross its border. When the rebels need weapons, they make their request at an “operations room” in Amman staffed by agents from Jordan, Saudi Arabia and the United States.

During more than three years of civil war in Syria, this desert nation has come to the world’s attention largely because it has struggled to shelter hundreds of thousands of refugees. But, quietly, Jordan has also provided a staging ground for rebels and their foreign backers on Syria’s southern front. In the joint Arab-American operations room in Amman, the capital, for example, rebels say they have collected salaries as an incentive not to join better-funded extremist groups.

But this covert aid has been so limited, reflecting the Obama administration’s reluctance to get drawn into another Middle Eastern conflict, that rebels say they have come to doubt that the United States still shares their goal of toppling President Bashar al-Assad. […]