It’s the top-secret mission that never was: the US plan to oust Syrian dictator Bashar al-Assad in 2012.

A former CIA agent named Douglas Laux reveals the Obama administration’s paralysis — and that of our European allies — in his heavily redacted new memoir, “Left of Boom” (St. Martin’s Press).

After meeting with members of the Syrian rebellion, Laux was summoned back to DC, where he briefed his superiors in June 2012.

“It became clear right away that everyone involved in the Syrian issue, from the White House on down, regarded it as a political hot potato,” Laux writes. “They wanted to aid the Syrian rebels, but were wary of being drawn into a war that could spread throughout the region and make them look bad politically.”

Still, Laux says he spent two months drawing up plans and traveling to European capitals, attempting to sway US allies into taking action. Like the rest of the book, names, dates, even whole conversations are blacked out — the result of CIA vetting before publication.

“It quickly became clear,” he writes, “that [our allies] wanted to support the program but expected us to do everything.”

On Aug. 10, 2012, then-Secretary of State Hillary Clinton traveled to Turkey and publicly announced that the US was seriously considering a no-fly zone over Syria.

Laux was stunned — the CIA had given him no heads-up, and he had no idea if they even knew about this announcement. He immediately met with Syrian rebel leaders who, he writes, “were elated by Clinton’s statement.”

Once suspicious of US motives in the region, they now “happily shared everything with me — the state of their forces, where they were deployed, the names of important leaders, etc. It yielded an intel bonanza.”

A week went by with no US air power over Syria. Two weeks, and the rebels were angry and suspicious, despite President Obama’s public statement that the use of chemical weapons in Syria would be “a red line,” resulting in likely military force.

‘What [the consideration a no-fly zone over Syria] accomplished was to flush the slim credibility we had in Syria down the drain’ - Douglas Laux

After three weeks, the rebels felt so betrayed that they stopped meeting entirely with Laux, who realized Clinton’s statement had been a bluff — a clumsy attempt to flush Assad out diplomatically.

“What it accomplished,” Laux writes, “was to flush the slim credibility we had in Syria down the drain.”

Laux returned to CIA headquarters in September. He was shocked to hear that both the CIA and the White House wanted specific plans drawn up on how to oust Assad.

By October, Laux writes, his task force had drafted and presented 50 options. He doesn’t reveal whether those options included assassination or simply removing Assad from power for exile or trial. He heard good feedback, but no action was taken — his own “stagmire.”

“It was immensely frustrating,” he writes. US allies in Europe and the Middle East were doing nothing while Russia, China and Iran actively backed Assad, causing more civilian deaths and the worst refugee crisis since World War II.

Laux knew what was going on, even if no one would admit it. He drafted one of his last memos, “suggesting that we change our end goal from removing Assad to backing away from the conflict . . . [since we] now appeared feckless and weak in the eyes of people all over the globe, we should pull out of the Syria crisis completely.”

Laux resigned from the CIA weeks after President Obama, in December 2012, walked back his comments on a red line.

“We’re kind of boxed in,” an administration official said at the time. “There’s an issue of presidential credibility here. But our options are quite limited.”