WASHINGTON — CIA operatives and U.S. special operations troops have been secretly training Syrian rebels with anti-tank and anti-aircraft weapons since late last year, months before President Obama approved plans to begin directly arming them, according to U.S. officials and rebel commanders. The covert U.S. training at bases in Jordan and Turkey, along with Obama’s decision this month to supply arms and ammunition to the rebels, have raised hopes among the beleaguered opposition that Washington ultimately will provide heavier weapons as well. So far, the rebels say they lack the weapons they need to regain the offensive in Syria’s bitter...