The Pentagon is putting the final touches on its proposal for establishing a Space Force — and it’s not quite as ambitious as the vision President Donald Trump turned into one of his signature rallying cries.

But the current version, considered a historic first step in elevating the military's space mission, is already getting a far more welcoming reception among Democratic and Republican skeptics on Capitol Hill.

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The latest plan calls for creating a sixth branch of the military, as Trump has proposed, by combining troops dedicated to space missions into a new armed service commanded by its own four-star general. But instead of the "separate but equal" Space Force that Trump advocated last year, it would fall under the purview of the Air Force, which would manage and host many of its operations and acquire most of its equipment.

The Space Force would be loosely modeled on the Marine Corps, which is overseen and funded by the Department of the Navy even though it operates independently. But it would have somewhat less stature than the Army, Navy and Air Force, each of which has its own civilian secretary, control over its budgets and a network of bases and training facilities. It would even lack some of the independence of the Marine Corps, which maintains its own bases.

The White House declined a request for an update on the deliberations. But several defense and administration officials said the White House has informally blessed the new proposal, which they describe as meeting the president's intent of a sixth military branch. And the approach is shaping up to be much more politically palatable on Capitol Hill than Trump’s original, more grandiose version.

"I actually think this is a promising proposal," House Armed Services Chairman Adam Smith (D-Wash.) told POLITICO in an interview. “Not sure we're going to do it, but we can certainly work with it. … That’s probably a good template to work off of, and then the devil is in the details.”

He added: "I believe that space needs to be emphasized.”

Senate Armed Services Chairman Jim Inhofe (R-Okla.), another early opponent, said he could go along with it, too, despite his initial misgivings about creating a Space Force. He said he would support some proposed structure if it could keep pace with Russian and Chinese advances more effectively than the status quo.

"I was opposed to it altogether because [what] we don’t need is another bureaucracy and we’re handling it pretty well right now," Inhofe told POLITICO. "But I would go ahead and support it."

"If we could do it, centralize this under the Air Force, that would probably accomplish the same thing," he added. "At least it centralizes it."

The plan has emerged after what several officials described as a bruising fight inside the Pentagon, where powerful interests were always wary of creating a new branch that could siphon off authority and dollars from current programs.

Early drafts of a White House directive prepared for Trump called for establishing a standalone Department of the Space Force with its own civilian secretary like the Army, Navy and Air Force.

Under the latest proposal, however, the Space Force would not be on par with those branches.

For example, it would not oversee the development of new space technologies as the Army, Navy and Air Force now do. It also would not wrap in an emerging Space Development Agency that Congress mandated last year to speed up the acquisition of new space technologies, officials said. That agency would initially be overseen by Michael Griffin, a former NASA administrator who is now undersecretary of defense for research and engineering.

Nor would the Space Force control its own military bases, according to several officials with direct knowledge of the deliberations.

The proposal does call for shifting thousands of Air Force, Army and Navy personnel that now carry out space-related missions into the Space Force, with a separate training system and four-star general as commander, who would be a member of the Joint Chiefs of Staff.

"It's going to be small — as small as possible footprint," acting Defense Secretary Pat Shanahan told reporters Tuesday. "That’s why it’s — you know, recommended it sits underneath the Air Force."

The plan has similarities to previous proposals in Congress to create a dedicated Space Corps within the Air Force, but not as a full-fledged military branch — proposals the Pentagon brass initially opposed.

"What's emerging appears to be the Space Corps concept — the Marine Corps kind of thing inside the Department of the Air Force," said Brian Weeden, a space expert at the Secure World Foundation in Washington who has closely followed the deliberations. "That makes the most sense, both from a bureaucratic process but also a political process.

"It is not as big of a lift as creating a whole new department," Weeden added. "You don't have to deal with all the same overhead problems — everything from doctors to sanitation, bases. They are trying to come up with a way to do something that can satisfy everyone, including the president," while "still letting it develop a unique culture and leadership cadre."

So far, the Pentagon appears to have won over Trump's advisers.

"There are a lot of things a [full-fledged] department would have to have," said one administration official who is involved in the discussions. "You pile on those things, it becomes a lot more hampered down. They are going to a low-cost solution. The plan that comes out will follow the president's vision. It is a well thought-out proposal that meets the president's intent.

"The bottom line is it will be the sixth branch of the military," the official added. "Everyone is on the same page."

That doesn't mean it is a sure thing in Congress.

"It depends on what expenses are attached to it," Inhofe told POLITICO. "There’s a way of making it cheaper … I wouldn’t want to commit to what he’s proposing now because we might get a better deal when it comes up."

And then there's the question of how much Trump's stamp on the Space Force could sour rank-and-file Democrats, especially in the House — no matter what the details.

"On one hand you can give Trump credit for elevating this issue and forcing the debate on it," Weeden said. "But the downside of that is wanting to put his name on it. So therefore for a significant portion of both politicians and the public, your view of this depends on your view of the president."