WASHINGTON — As President Trump prepares to meet Kim Jong Un of North Korea to negotiate denuclearization, a challenge that has bedeviled the world for years, he is doing so without the help of a White House science adviser or senior counselor trained in nuclear physics.

Trump is the first president since 1941 not to name a science adviser, a position created during World War II to guide the Oval Office on technical matters ranging from nuclear warfare to global pandemics.

As a businessman and president, Trump has proudly been guided by his instincts. Nevertheless, people who have participated in past nuclear negotiations say the absence of such high-level expertise could put him at a tactical disadvantage in one of the weightiest diplomatic matters of his presidency.

“You need to have an empowered senior science adviser at the table,’’ said R. Nicholas Burns, who led negotiations with India over a civilian nuclear deal during the George W. Bush administration. “You can be sure the other side will have that.’’

The lack of traditional scientific advisory leadership in the White House is one example of a significant change in the Trump administration: the marginalization of science in shaping US policy.

There is no chief scientist at the State Department, where science is central to foreign policy matters such as cybersecurity and global warming.

Nor is there a chief scientist at the Department of Agriculture: Trump last year nominated Sam Clovis, a former talk-show host with no scientific background, to the position, but he withdrew his name and no new nomination has been made.

These and other decisions have consequences for public health and safety and the economy. Both the Interior Department and the National Oceanic and Atmospheric Administration have disbanded climate science advisory committees.

The Food and Drug Administration disbanded its Food Advisory Committee, which advised on food safety.

At the same time, government-funded scientists said in interviews that they are now seeing signs that their work is being suppressed, and they are leaving their government jobs to work in the private sector, or for other countries.

After Trump last year withdrew from the Paris climate agreement, France launched a program called “Make Our Planet Great Again’’ — named in reference to Trump’s slogan, “Make America Great Again’’ — to lure US scientists to France.

The program has so far provided funding for 24 scientists from the United States and other countries to do their research in France.

The White House declined to comment on these and other suggestions that the role of science in policymaking has been diminished in the Trump administration.

Regarding this week’s talks with Kim, a spokesman for the White House’s National Security Council, Garrett Marquis, emphasized that “the president’s advisers are experts in their fields.’’

The larger matter, though, is the president’s lack of a close senior adviser at the White House level — someone who has Trump’s trust and his ear — said Michael Oppenheimer, a professor of geosciences and international affairs at Princeton.

“I don’t think there’s ever been a time in the post-World War II period where issues as important as nuclear weapons are on the table and there is no serious scientist there to help the president through the thicket,’’ he said. “This reverberates throughout policy.’’

The most pressing geopolitical need may be in the realm of nuclear diplomacy.

While the State Department declined to characterize the makeup of its preparatory team for Tuesday’s North Korea meeting, Trump could of course tap any number of government nuclear physicists to accompany him.

And Marquis, the Security Council spokesman, emphasized that many of the president’s advisers “have advanced degrees and have worked on these complex issues in and out of government.

The materials that have gone to the president ahead of the negotiation reflect the work of more than a dozen people at the PhD level in relevant fields,’’ he added, including “at least one’’ in nuclear engineering.

A State Department spokeswoman referred questions to the National Security Council.

Nevertheless, as Trump prepares for the talks, he has no close aides on par with those who helped President Barack Obama negotiate a nuclear deal with Iran.

Obama’s advisers included Ernest J. Moniz, a nuclear physicist who led the Energy Department and oversaw the nation’s nuclear weapons arsenal, and John Holdren, a physicist and expert in nuclear arms control who served as the White House science adviser.

“There is going to be the requirement for trade-offs, and that judgment is best made by people with technical expertise who are also very senior politically,’’ Moniz said. “That just does not exist in this administration.’’

As for Kim, “The North Korean nuclear scientists are very, very competent, and I would expect them to advise their government well,’’ said Siegfried S. Hecker, a former director of the Los Alamos weapons laboratory in New Mexico and an expert on North Korea’s nuclear weapons program.

In Washington, the administration’s excising of science is particularly evident at the Environmental Protection Agency.

Scott Pruitt, the embattled head of the EPA, has initiated more than a dozen regulatory rollbacks, including signing a measure declaring his intent to undo or weaken Obama’s climate change regulations known as the Clean Power Plan.

However, his more enduring legacy may be in diminishing the role of academic, peer-reviewed science at the agency.

In April, he proposed a regulation that would dramatically limit the types of research that EPA officials could take into account when crafting new public health policies, a change that could weaken the agency’s ability to protect public health.