WASHINGTON — Sen. Jim Inhofe, a key skeptic on U.S. President Donald Trump’s proposed Space Force, said Tuesday that Defense Secretary Jim Mattis has nearly convinced him a new branch would be a good idea. But, he added, the cost will be a factor.

“He did almost, a little bit,” Inhofe, R-Okla., said of conversation with Mattis on the topic last week. Russian and Chinese investment in space may justify it, Inhofe said, adding: "They’re our top competitors. ... By us not having one, there could be an argument we’re not as committed to space as they are. Now that isn’t true.”

Trump, in June and again this month, announced his intent to create a sixth branch for space with Congress’ help, but several key lawmakers have voiced skepticism, if not opposition. That group includes Inhofe, who is expected to be named the next Senate Armed Services Committee chairman at some point soon after Sen. John McCain’s funeral this week.

On Tuesday, Inhofe said he’s open to “a separate bureaucracy ... without having to spend billions of dollars on it.” But without the details, he wasn’t ready to commit. “We don’t know the ingredients yet. We don’t know what the cost would be. When that time comes, we’ll take a position,” he said.

At a Pentagon news briefing Tuesday, Mattis and Joint Chiefs of Staff Chairman Gen. Joe Dunford said they do not yet have a cost estimate for establishing a new branch.

Both men said the cost for a Space Force is unknown. “We don’t have a full cost right now,” Dunford said.

The interim step — setting up a combatant command focused on space issues — “will not be that expensive because we’ll build out on what we have right now,” Mattis said.

Dunford added that he met with stakeholders Monday in the Defense Department to work on details about standing up the command structure.