Only four or five Syrian individuals trained by the United States military to confront the Islamic State remain in the fight, the head of the United States Central Command told a Senate panel on Wednesday, a bleak acknowledgment that the Defense Department's $500 million program to raise an army of Syrian fighters has gone nowhere. Gen. Lloyd J. Austin III, the top American commander in the Middle East, also told the Senate Armed Services Committee that the United States would not reach its goal of training 5,000 Syrian fighters anytime soon. In May, the Defense Department began its training program for up to 5,400 fighters a year, in what White House officials described as a necessary component of President Obama's strategy to use local troops on the ground against the Islamic State. General Austin told the Senate committee that many fighters in the first class of 54 graduates of the training program for Syrians were attacked in July by an offshoot of Al Qaeda, the Nusra Front, and either fled or were killed, leaving only a small number" of rebels still in the fight. Asked how many fighters were still in Syria, General Austin said that "it's a small number." He added, "We're talking four or five."