Only 5 feet 6 inches and weighing 120 pounds, Abdella Ahmad Tounisi wasn’t even sure he could cut it as a fighter for the cause.

Nevertheless, the tiny would-be terrorist — wearing a jail jumpsuit with the legs rolled up — pleaded guilty in federal court Tuesday to attempting to provide material support to a foreign terrorist organization.

When U.S. District Court Judge Samuel Der-Yeghiayan asked Tounisi, 21, specifically what he’d done, the soft-spoken Aurora man said: “I tried to go to Syria to fight with Jabhat al-Nusrah, knowing it was a designated terrorist organization.”

As he spoke, some three dozen family members — including a toddler and a baby — and supporters looked on in the courtroom gallery.

Tounisi now faces up to 15 years in prison at his sentencing, set for Dec. 9

Tounisi’s guilty plea comes just two months before his friend, Adel Daoud, is set to go on trial for a September 2012 plot to blow up a bar in downtown Chicago. Tounisi allegedly helped Daoud plan that attack, but he backed out when he became suspicious about an accomplice who turned out to be an undercover federal agent.

Federal officials said Tounisi’s “interest in violent jihad continued, notwithstanding Daoud’s arrest.” Authorities nabbed him at O’Hare Airport in April 2013, where he allegedly planned to travel to war-torn Syria and hoped to join a “jihadist militant group.” The U.S. citizen had gone through airport security, headed for a flight to Istanbul, Turkey, they said.

Tounisi hoped to join Jabhat al-Nusrah, a group affiliated with al-Qaida, according to the FBI. He was charged with attempting to provide material support to a foreign terrorist organization.

The feds caught Tounisi in an Internet sting after he contacted a sham website set up by the FBI that purported to hook up would-be fighters with terrorists, according to the federal criminal complaint against him.

Between January and April 2013, Tounisi searched online for information about travel from Chicago to Syria, obtained a new passport and, beginning in late March 2013, made contact through the website with someone he thought was a recruiter for Jabhat al-Nusrah but who was actually an FBI agent.

The top of the website said “A Call for Jihad In Syria,” and it asked would-be fighters to “come and join your lion brothers of Jabhat Al-Nusra who are fighting under the true banner of Islam, come and join your brothers, the heroes of Jabhat Al-Nusra,” according to the complaint.

In email exchanges with the undercover FBI agent, Tounisi described his plan to get to Syria through neighboring Turkey and spoke of “his willingness to die for the cause,” according to authorities.

He was frank with the purported recruiter, according to the FBI. In one email Tounisi wrote, “Concerning my fighting skills, to be honest I do not have any. I’m very small . . . physically but I pray to Allah that he makes me successful,” according to the complaint.

Email responses to Tounisi from the undercover agent referred to Tounisi as “Brother Abdullah” and encouraged him not to despair about his lack of battle skills.

Authorities said Tounisi believed he would be joining Jabhat al-Nusrah. Late in 2012, the U.S. State Department designated Jabhat al-Nusrah a foreign terrorist organization, saying it was an alias for al-Qaida in Iraq. The organization had taken credit for hundreds of terrorist attacks.

According to the criminal complaint against him, Tounisi also conducted Internet searches for the phrases “martyrdom operations,” “providing material support what does it mean” and “Terrorism Act 2000.”

Contributing: Jon Seidel