Secretary of State Marco Rubio and Elon Musk, the tech billionaire deputized by President Trump to slash federal spending, sought to smooth over their ugly confrontation in the White House last week with an awkward social media embrace on Monday, as Mr. Rubio formalized deep cuts to foreign aid that Mr. Musk had demanded.

Mr. Rubio and Mr. Musk clashed during a meeting in the Cabinet Room of the White House last Thursday, in which the world’s richest man jeered the secretary of state for failing to make more sweeping staffing cuts to the agencies under his purview. In the same meeting, Mr. Rubio bristled at how Mr. Musk had undercut his leadership to flatten the U.S. Agency for International Development, the government’s lead agency for distributing foreign aid.

On Monday, Mr. Rubio thanked Mr. Musk’s team at the Department of Government Efficiency for aiding in making the drastic cuts he had resisted, and announced that the agency’s remaining work would be subsumed under the State Department.

Mr. Rubio wrote on his personal account on X, the social media platform owned by Mr. Musk, that 83 percent of U.S.A.I.D.’s programs were being cut. “The 5200 contracts that are now cancelled spent tens of billions of dollars in ways that did not serve, (and in some cases even harmed), the core national interests of the United States,” he added.

Mr. Musk replied: “Tough, but necessary. Good working with you.”

During the meeting last week, Mr. Trump defended Mr. Rubio for doing a “great job” and decreed that Mr. Musk’s team would be merely advising Cabinet secretaries about future cuts. But Mr. Rubio’s apparent embrace of Mr. Musk’s objectives revealed the extent to which the billionaire Trump supporter wields power in the administration.

Mr. Rubio’s announcement appeared to be the official culmination of the process of culling foreign aid that had been underway for weeks, as Mr. Musk led the charge to greatly reduce the footprint of U.S.A.I.D., which manages about $42.5 billion in global assistance programs that represent less than 1 percent of the annual federal budget. The moves, which included canceling contracts, turning off payment systems, and laying off or forcing the vast majority of staff onto administrative leave, crippled the agency and left the global humanitarian aid industry that relied on the agency’s funding in limbo.

Mr. Trump had announced in an executive order on the first day of his presidency that he was instituting a 90-day pause on foreign aid, pending a review, to bring the United States’ foreign aid programs in line with his administration’s interests. But the cuts to U.S.A.I.D. prompted a series of lawsuits from the unions representing agency staff members and the organizations that were stiffed by the cuts.

One of those cases rose to the Supreme Court, which ruled last week that the administration had to comply with a lower court’s ruling to release the frozen funds — even though the Supreme Court did not specify exactly how much of the nearly $2 billion in contracts in question had to be restored.

The plaintiffs in several lawsuits, as well as other critics of the Trump administration’s maneuvers, have derided the moves as illegal, arguing that the law that created U.S.A.I.D. means that only Congress can significantly reduce its budget.

They have also argued that the cuts are shortsighted, and will lead to widespread human suffering and ultimately hurt U.S. national security.

Among the affected projects are those that deal with food security and famine warnings, agricultural efficiency, women’s health, L.G.B.T.Q. communities, and civil society and energy in war-torn Ukraine, according to a list of the canceled contracts shared with members of Congress last week, copies of which were obtained by The New York Times.

In recent days, some health-related groups — many of which help distribute H.I.V. medication — have had their funding restored.

The Trump administration has said in court filings that its review of programs was complete, but several organizations recently received questionnaires asking them to justify how their contracts lined up with U.S. interests. Deadlines for responding were as late as March 17.

Robert Jimison and Stephanie Nolen contributed reporting.