WASHINGTON — A professor at the American University of Beirut traveling to California for an engineering conference says he was wrongfully denied entry to the US because of new “extreme vetting” measures.

George A. Saad, 35, an associate professor at the Lebanon campus, missed his Monday presentation at the Engineering Mechanics Institute Conference in San Diego because Department of Homeland Security officials turned him away at Los Angeles International Airport without explanation, he told The Post.

When he landed Friday, Saad said he was detained and interrogated for four hours. His phone was confiscated and his laptop was seized and he had to divulge passwords for his devices. He was photographed and fingerprinted.

Saad said his visa was revoked and he was put on the next plane back toward Beirut without an opportunity to contact a lawyer or his worried wife.

“I belong to the American University of Beirut — the leading academic institution in Lebanon and the Middle East, chartered in New York and considered an American territory in Lebanon,” Saad told The Post. “I felt so small, so unappreciated and consider being treated in demeaning and humiliating ways.”

Although courts have blocked President Trump’s travel ban, his administration is pushing ahead with enhanced screening measures. State Department consular officers have stepped up questioning of visa applicants and are vetting social media activity. Homeland Security officials have increasingly used their removal and detention authority, employed more aggressive screenings at airports and have stepped up searches of travelers’ laptops and smartphones, according to immigration experts.

Saad earned his master’s degree from Johns Hopkins University and his doctorate from the University of Southern California. Saad said he is Christian, has family in America and no criminal record.

He’s traveled to the US about 15 times without incident and had no trouble attending similar engineering conferences in 2015 and 2016, Saad said.

Jonathan Meyer, former deputy general counsel at Homeland Security under President Barack Obama, said the agency does not necessarily tell travelers why they are denied entry, and in some cases they can’t. But, given his frequent visits to the US in the past, Saad’s new travel troubles seem a bit “odd.”

“We don’t know exactly what information [the Customs agency] is relying on, but this case is compelling in that there does not seem to be an issue here,” said Meyer, a partner at Sheppard, Mullin, Richter & Hampton LLC.

Whether Trump’s tough demands for extreme vetting could be the reason for Saad’s denial, Meyer said there’s no way to know definitively.

“His rejection after years of admission may provide some evidence,” Meyer said. “[Saad] has to be asking himself would this be happening if his last name weren’t Saad or if he weren’t from Lebanon?”

Saad already filed a formal complaint with Homeland Security’s Traveler Redress Inquiry Program so he can come to the conferences in the future, but he’s out the $2,500 cost of the trip.

Complaints over gaining entry into the US have increased 10.5 percent from this point last year: 6,078 from January to May 2017, compared to 5,500 during the same time in 2016. There were 5,985 in the comparable period in 2015.

Neither Homeland Security nor US Customs and Border Protection offered information on why Saad was denied entry to the US.

The American University of Beirut, which has its US corporate office in the New York, stands by its professor.

“While we understand and respect security measures, we are surprised and concerned at the treatment our faculty member received, including his long interrogation followed by denial of his entry into the US,” the university said in a statement to The Post.

“We stand firmly behind the free movement of genuine and peaceful scholars to share their data globally, as part of our firm commitment to academic freedom and to the open exchange of ideas.”