The Obama administration has ended the Pentagon’s $500 million program to train and equip Syrian rebels, administration officials said on Friday, in an acknowledgment that the beleaguered effort had failed to produce any kind of ground combat forces capable of taking on the Islamic State in Syria. Pentagon officials announced the end of the program on Friday, as Defense Secretary Ashton B. Carter left London after meetings with his British counterpart, Michael Fallon, about the continuing wars in Syria and Iraq. The closing of the program comes as the administration’s attention is shifting to northeastern Syria, where it hopes to assemble a group of Sunni tribes in a “Syrian Arab Coalition” to fight alongside Syrian Kurdish forces against the Islamic State, also known as ISIS or ISIL. “Secretary of Defense Ash Carter is now directing the Department of Defense to provide equipment packages and weapons to a select group of vetted leaders and their units so that over time they can make a concerted push into territory still controlled by ISIL,” a Pentagon statement said of the new effort. The statement said the Pentagon would monitor the progress of these groups “and provide them with air support as they take the fight to ISIL.”