WASHINGTON — John Brennan was headed for the priesthood when, while sitting idly on a bus as a student at Fordham University in the 1970s, he stumbled on a recruiting ad for the Central Intelligence Agency.
Now, after years of poring through intelligence, trekking with Mideast tribesmen, and overseeing some of America’s most controversial counterterror missions, he is pursuing a calling with as much responsibility and arguably a lot more stress — director of central intelligence.
President Obama on Monday nominated Brennan, his antiterrorism chief, to head the CIA. It is the second time that Brennan has made a run for the job.
Obama called Brennan, who advised his 2008 presidential campaign, ‘‘one of my closest advisers’’ and ‘‘a great friend’’ whom he credited with hobbling Al Qaeda and terrorist threats to the United States. ‘‘He is one of the hardest-working public servants I’ve ever seen,’’ the president said. ‘‘I’m not sure he’s slept in four years.’’
Brennan, a stern-looking man who nonetheless salted a few wry quips into his brief comments at the White House, pulled himself out of consideration for the top spying job in 2008 after being accused of supporting a terrorist interrogation program that critics called a form of torture.
Within weeks, however, Obama ensconced Brennan as his top homeland security and counterterrorism adviser, giving the veteran intelligence officer a far broader portfolio — and grasp of power — than he would have had at the CIA.
Now, the White House says Brennan has since helped end the harsh programs and wants to send him back to Langley, Va., where the CIA is based outside Washington.
‘‘Leading the agency in which I served for 25 years would be the greatest privilege as well as the greatest responsibility of my professional life,’’ Brennan, 57, said in accepting the nomination. He promised to make the agency’s highly secretive programs as transparent as possible, without risking security, to preserve public trust.
During his years at the CIA, Brennan was an analyst and intelligence officer and served as station chief in Saudi Arabia and as President Clinton’s daily intelligence briefer.
As director, he would replace General David Petraeus, who left in November after admitting to an affair with his biographer.
During Obama’s first term, Brennan handled an array of matters, including drone strikes in Pakistan, the thwarted attack by underwear bomber Umar Farouk Abdulmutallab in Detroit, rampant US mass shootings, and the federal response to Hurricane Sandy.
He has also been dubbed the unofficial ambassador to Yemen for his frequent interplay with the Sana government over rehabilitating detainees from the Navy prison at Guantanamo Bay, as well as burgeoning threats from local Al Qaeda militants.
Though it is believed he will be easily confirmed, Brennan is expected to face pointed questioning in the Senate about the US drone program, which has resulted in some civilian deaths and strained diplomacy in its pursuit of militants in Pakistan, Somalia and Yemen.
He will also be needled about the interrogation program that kept him from heading the CIA four years ago. Brennan has since disavowed at least some of the agency’s interrogation methods, including waterboarding, which simulates drowning.
When he withdrew his name from consideration in 2008, Brennan said he was not involved with the decision-making process about the program or other methods of curbing terrorism, including renditions — spiriting foreign suspects to nations where there are no or few laws preventing torture.
Ben Rhodes, Obama’s deputy national security adviser, predicted that the interrogation issue would not be a matter of debate since Brennan helped end the program while at the White House. But Republican Senator John S. McCain, a member of the Senate Armed Services and Foreign Relations committees, said Monday he plans to resurrect the matter during confirmation.
Senate Intelligence chairwoman Dianne Feinstein, whose committee will hold hearings to consider Brennan’s nomination, said she too will pursue answers about the interrogations program, which was adopted shortly after 9/11.
But she predicted that Brennan will sail through confirmation: ‘‘I believe he will be a strong and positive director,’’ the California Democrat said.