WASHINGTON- Matthew G. Olsen, the director of the National Counter-Terrorism Center, is resigning after three years, a time during which the threat from Al Qaeda shifted from its headquarters in Pakistan to its affiliates in places like Syria, Iraq and Yemen. “Most Americans may not know Matt Olsen’s name, but every American is safer because of his service,” President Obama said in a statement released by the White House. A spokesman for the counterterrorism center echoed comments from Mr. Olsen’s friends and colleagues, who said his decision to step down “was a personal one for him and his family.” He has not set a date to leave the job, which he assumed in August 2011, but he is expected to depart in the next few months, after a successor is selected, the spokesman said. Mr. Olsen, 52, is a former general counsel for the National Security Agency with extensive experience in intelligence matters, and after a 24-year career in government, he has told friends and colleagues that he would like to take a job outside it. Mr. Olsen has been a leader in warning about the threat posed by radicalized young Muslims with Western passports who have traveled to Syria to fight the government of Bashar al-Assad. “As Al Qaeda morphed after the death of Bin Laden, Matt kept the focus on the new environment,” said Michael E. Leiter, Mr. Olsen’s predecessor. Mr. Olsen was inadvertently caught in the controversy over the attacks on the United States Mission in Benghazi, Libya, in 2012, telling a congressional committee that Ambassador J. Christopher Stevens and three other Americans had died “in the course of a terrorist attack.” It was only after Mr. Olsen’s unscripted comments that White House officials also began publicly calling the assault a terrorist attack, all of which fueled criticism from Republican lawmakers, who said the administration had been playing down a threat for which it was unprepared.