As recently as last month, Gen. James “Hoss” Cartwright was known in Washington as “Obama’s favorite general,” a leading candidate to become the country’s top military officer, and one of the biggest tech fiends ever to pin four stars to his shoulders. Now, Cartwright has been definitively ruled out as the next chairman of the Joint Chiefs of Staff, Pentagon sources tell Danger Room — the apparent victim of a nasty Beltway whisper campaign.

It means that the military leadership will be losing one of its more original thinkers, just as the Pentagon reconsiders, well, everything: the Afghanistan war, a growing rivalry with China, a budget that could get cut by $400 billion or more.

“General Cartwright is unique. He has a quick, intuitive grasp of technologies and their military applications. And he has an equally impressive ability to clearly explain them to his counterparts in the services,” former Darpa director Tony Tether e-mails Danger Room. “All four-stars I have met have been exceptional people, for many different reasons. But only Cartwright has this particular combination.”

Gen. Martin Dempsey — sworn in just last month as chief of staff of the Army — is now considered the top contender for the chairmanship. An announcement is expected next week, when President Obama returns from his European trip. No decision is final, Pentagon sources say. But Cartwright is definitely out.

Cartwright, a former F/A-18 pilot and fellow at MIT, emerged on the national scene as the head of U.S. Strategic Command, which oversees America’s nuclear forces. Cartwright re-imagined the Command’s “global strike” mission as something much bigger than nukes.

He expanded the notion to include commandos, conventionally armed missiles, and (especially) electronic attacks. As the military wrestled with how to break up and infiltrate insurgent communications networks in Iraq and Afghanistan, Cartwright became an influential champion.

In 2005, when many in the Defense Department were running away from social media, Cartwright started a blog, and told his troops at StratCom to do the same. Two years later, he was interviewed wearing a “100 blogs” patch on his flight suit.

When the Pentagon needed to shoot a dying satellite out the sky in 2008, Cartwright rode herd over the operation. When Defense Secretary Robert Gates wanted to radically overhaul the Pentagon’s arsenal, Cartwright was one of a small handful of advisers that cooked up the plan to make it happen.

When the military scratched its collective head over how to handle network threats, Cartwright was instrumental in setting up U.S. Cyber Command. By 2009, he was calling old-school missile defense “as passé as e-mail.”

The comfort with technology helped Cartwright rise to the post of vice chairman of the Joint Chiefs of Staff — the nation’s No. 2 military officer. In the job, he helped craft a compromise on the U.S. troop “surge” in Afghanistan, despite his lack of combat experience. And he continued his patronage of Darpa, the military’s way-out research arm, and pushed agency projects in hypersonics, automated language translation, and battlefield information-sharing.

Sometimes, Cartwright seemed to be too technophilic for his own good. The physics of his push for conventional “global strike” missiles may have worked. But the geopolitics were terrible, counting on Russia and China to take America’s world that the missiles were neither nuclear nor aimed at them.

But Cartwright’s ascent doesn’t seem to have been stopped by his occasional screwball, or even by his lack of war-zone experience. In Washington, rumors persisted that Cartwright had romantic relationships with women who were not his wife. Nobody could prove those allegations. In fact, a Pentagon inspector-general report cleared him of the charge that he had an affair with a female aide.

But that didn’t stop the innuendo from continuing to ooze. During my 24-hour trip to Washington last week, three separate people brought up Cartwright’s “zipper problem,” noted his separation from his wife, and connected him to all sorts of leading women in the military establishment. None of these people had first-, second- or even third-hand knowledge of these alleged dalliances.

So why the whisper campaign? At the risk of being a rumormonger myself, I’d note — as Spencer Ackerman did in this blog last February, the last time the Cartwright gossip crested — that Cartwright made many in the military establishment uncomfortable.

He lobbied to give the Vice Chairman’s office unparalleled power over decisions about which weapons the Pentagon should buy. He worked with Vice President Biden to come up with alternatives to the surge in Afghanistan, even when the buildup was accepted Pentagon wisdom.

He pushed to kill the F-22 Raptor and scrap new testing for the country’s nukes. In Air Force circles, he’s blamed for paring back plans for a new, strategic bomber fleet.

Cartwright ordered his staff not to lobby on his behalf for the Chairmanship. But one of his foes, it now appears, waged an entirely different sort of campaign.

Photo: U.S. Air Force