Mark Green, new head of USAID, in his office, on August, 11. A new report argues against merging USAID with the State Department. (Bill O'Leary/The Washington Post)

A bipartisan group of former diplomats and other officials warned Thursday against a merger of the roles of the State Department and the U.S. Agency for International Development in international crises as part of the restructuring and budget cuts planned by the Trump administration.

U.S. efforts to help refugees in particular would be jeopardized by some of the proposals that Secretary of State Rex Tillerson and the White House have considered, a report signed by former deputy secretary of state William J. Burns and others argued.

“Consolidation of the functions of either agency into the other would be a significant error,” the report advises. “Each has functions that are inherent in its organizational mission.”

A copy of the report from Refugees International was provided to The Washington Post ahead of its release. It recommends that the two agencies operate with greater collaboration while remaining distinct and strongly advises against eliminating the State Department bureau that deals with refugees.

“We are deeply concerned by proposals which would effectively end the State Department role in international humanitarianism,” the authors wrote.

One proposal would send the Bureau of Population, Refugees and Migration’s refugee assistance functions to the Department of Homeland Security.

Such a shift would “send an obvious and powerful signal, within the United States and to the rest of the world, that the United States is diminishing its historical concerns about the displaced and disenfranchised,” and may undermine a 1980 law on U.S. treatment of refugees, the report said.

“This would ill-serve U.S. interests and would be a betrayal of the values that have characterized our nation from its very founding,” the authors wrote.

The report is signed by former political appointees from the George W. Bush and Barack Obama presidencies, as well as retired senior diplomats such as R. Nicholas Burns.

The U.N. High Commissioner for Refugees last year reported that more than 65 million people have been forcibly displaced around the world, the highest number the agency has recorded.

The Trump administration has sought to temporarily shut down the nation’s refugee program and bar visitors from several majority-Muslim countries while officials examine vetting procedures.

The Supreme Court is to hear arguments on the merits of a challenge to the administration’s travel ban on Oct. 10. The high court last month decided on a new compromise over Trump’s travel ban, saying the government for now may enforce tight restrictions on refugees, but also must make it easier for people from six mostly Muslim countries to enter the United States.

The justices put on hold a part of a lower court’s order that would have made it easier for more refugees to enter the country. That order could have granted entry to about 24,000 refugees who were already working with resettlement agencies through programs administered by the State Department.

Legal challenges claim the ban is an unconstitutional effort at keeping out Muslims, a policy that Trump had advocated during the presidential campaign.

“Repeatedly in recent decades, the Department of State’s capacity to tightly integrate diplomacy with the tools of humanitarian assistance and refugee resettlement has been critical to achieving outcomes favorable to the United States,” the report said.

The Trump administration’s choice of Mark Green, a former congressman from Wisconsin, as the head of USAID won praise from Republicans and Democrats, and it eased some concern in Congress that the agency would be dismantled. At Green’s confirmation hearing, however, he said that he cannot predict what decision might be made and noted that USAID’s mission will have to adapt to smaller budgets.

The Trump administration has proposed cutting nearly one-third of the State Department’s budget and almost 40 percent from USAID, a $10 billion reduction, to $15.4 billion. Congress is unlikely to approve such deep cuts, but USAID’s funding level is almost certain to drop.