Counterterrorism experts have long suspected Saudi Arabia’s “rehabilitation” center for terrorists does a poor job of de-radicalizing jihadists. But a Saudi detainee at Guantanamo Bay now reveals it’s actually a recruiting and training factory for jihad.

According to recently declassified documents, senior al Qaeda operative Ghassan Abdullah al-Sharbi told a Gitmo parole board that the Saudi government has been encouraging previously released prisoners to rejoin the jihad at its terrorist reform school, officially known as the Prince Mohammed bin Naif Counseling and Care Center.

The Obama administration has praised the effectiveness of the Saudi rehab program — which uses “art therapy,” swimming, ping-pong, PlayStation and soccer to de-radicalize terrorists — and conditioned the release of dozens of Gitmo prisoners, including former Osama bin Laden bodyguards, on their enrollment in the controversial program.

To date, 134 Saudi detainees have been transferred to the Saudi reform camps in Riyadh and Jeddah. Last year, nine Yemeni detainees were sent there, as well, and more are expected to follow over the next two months, as President Obama strives to meet his campaign goal of closing Gitmo.

Al-Sharbi dropped a bombshell on the Gitmo parole board at his hearing earlier this year when he informed members that the Saudi kingdom was playing them for suckers. “You guys want to send me back to Saudi Arabia because you believe there is a de-radicalization program on the surface.

“True. You are 100 percent right, there is a strong — externally, a strong — de-radicalization program. But make no mistake, underneath there is a hidden radicalization program,” al-Sharbi added. “There is a very hidden strong — way stronger in magnitude — broader in financing, in all that.”

Al-Sharbi is one of the longest-serving, and most unrepentant, prisoners at Gitmo. A Saudi national with an electrical engineering degree from King Fahd University, he attended a US flight school associated with two of the 9/11 hijackers. He traveled to Afghanistan in the summer of 2001 and trained at an al Qaeda camp, building IEDs to use against allied forces.

Al-Sharbi was captured March 28, 2002, at an al Qaeda safehouse in Faisalabad, Pakistan, with senior al Qaeda leader Abu Zubaydah. According to his US intel dossier, he told interrogators that “the US got what it deserved from the terrorist attacks on 9/11.”

Given a chance at parole after 14 years, however, al-Sharbi was surprisingly frank with the board.

He explained that Riyadh is actively recruiting and training fighters to battle Iranian elements in neighboring Yemen and Syria. Saudi views Shiite-controlled Iran as a regional threat to its security.

“They’re launching more wars and the [United] States is backing off from the region,” he said. “They’re poking their nose here and here and there and they’re recruiting more jihadists, and they’ll tell you, ‘Okay, go fight in Yemen. Go fight in Syria.’ ”

Al-Sharbi said the Saudis also are “encouraging” former detainees “to fight their jihad in the States.”

“It’s not like a past history,” he said. “It’s increasing.”

A growing body of evidence backs up his claims. Last month, for example, a WikiLeaked email from Hillary Clinton revealed, citing US intelligence sources, that Saudi Arabia has provided “clandestine financial and logistic support to” ISIS and other Sunni terrorist groups in the region.

Al-Sharbi said the kingdom is playing a double game.

“They will proudly tell you they will fight terrorism,” he said. “That means they will support it.”

Al-Sharbi told the Gitmo board he doesn’t want to enroll in the Saudi rehab program, because he would be used to “fight under the Saudi royal cloak.”

“This is in the cause of a king. This is not a true jihad,” he said. “And I’m not going to Saudi unless I am sure they’re not gonna be using me.”

The Saudi rehab ruse has carried a lot of weight with the Gitmo parole board. Earlier this year, it released “Saudi al Qaeda recruiter and fighter” Muhammed Al Shumrani after his lawyers insisted that repatriating him to Saudi Arabia and enrolling him in its “well-established reintegration program” would cure his admittedly “problematic behavior.”

Last year, the defense team of longtime bin Laden bodyguard Abdul Rahman Shalabi insisted that the same Saudi rehab program would make sure he’s reformed. In approving his release, the board said that it was “confident about the efficacy of the Saudi program.”

In both cases, US intelligence warned the board that the hardened terrorists would more than likely “re-engage in terrorist activity.”

By Riyadh’s own numbers, some 20 percent of the terrorist enrollees at its rehab club — which features golf carts, palm trees and an Olympic-size pool — go back to the jihad, returning to the ranks of the Taliban or al Qaeda. US officials believe the recidivism rate is much higher, but Saudi Arabia does not disclose criteria for evaluation.

One high-profile failure was Said Ali al-Shihri. After his graduation from the Saudi program, he returned to Yemen, where he ran an al Qaeda branch and helped plan the deadly bombing of the US Embassy and mastermind the failed plot to blow up a 2009 Christmas flight over Detroit, before a drone-fired missile finally caught up to him.

The Saudi center is more holiday resort than halfway house for paroled inmates. Jihadists are rewarded with gourmet meals, video games, ping-pong, jacuzzis and newly furnished private apartments reserved for conjugal visits. They also are allowed unescorted visits to family members. In September, the center granted “beneficiaries” Eid al-Adha holiday vacation for 12 days.

Graduates are further rewarded with young brides and new cars.

Lending credence to al-Sharbi’s charges, the three-month program includes a few hours a day of lessons in Islam from Saudi clerics and “Shariah specialists.”

“Beneficiaries spend 15 hours a week in the Shariah program,” according to a local Jeddah press report, which is triple the amount of time devoted to psychological counseling.

Al-Sharbi’s parole was declined; he is still in Gitmo, along with 60 detainees — down from the 241 who were there when Obama started his term.

But with the administration rushing to reduce that number even further before the end of Obama’s term, how many more jihadists will be released into this highly suspect program?

Congress has an obligation to ask hard questions: Is this a pre-emptive campaign to prevent terror attacks or more likely an incubator for facilitating more attacks?

Paul Sperry is author of “Infiltration: How Muslim Spies and Subversives Have Penetrated Washington.”