In unveiling a panel to study the future of warfare this week, Defense Secretary Pete Hegseth did more than announce some advisers. He brought Elon Musk, the world’s richest man, back into the Trump administration fold.

With him came a raft of potential new conflicts of interest.

Mr. Musk had largely failed at his high-profile government cost-cutting expedition last year, not coming close to meeting his stated goals and leaving some agencies in disarray. After departing government duty, he prompted an epic fight with President Trump and threatened to start his own political party.

But after a long make-nice campaign, Mr. Musk is back in Washington with a seat at the table of the Pentagon, as a co-director of a group advising an agency that is a source of his vast personal wealth. As before when he was a special government employee, Mr. Musk’s appointment immediately set off concerns about whether he would have too much sway over decisions affecting his interests and those of his allies.

“It’s extraordinary to see the return without any recognition of the exceptional harm that he was responsible for in round one,” said Max Stier, the chief executive of the Partnership for Public Service, a nonpartisan organization that estimates that Mr. Musk’s cost-cutting efforts, dubbed the Department of Government Efficiency, cost each taxpayer more than $1,000 last year in waste.

Now, added Mr. Stier, “there’s no question that his financial interests are directly engaged in the position he’s going to fill here.”

Other members of the panel have major defense contract interests, including another co-director, Palmer Luckey, the founder of Anduril, which makes semiautonomous fighter jets. (Representatives from legacy defense companies, like Lockheed Martin and Raytheon, are largely absent.)