Allies of Donald J. Trump are proposing that the United States restart the testing of nuclear weapons in underground detonations should the former president be re-elected in November. A number of nuclear experts reject such a resumption as unnecessary and say it would threaten to end a testing moratorium that the world’s major atomic powers have honored for decades.

In the latest issue of Foreign Affairs magazine, Robert C. O’Brien, a former national security adviser to Mr. Trump, urges him to conduct nuclear tests if he wins a new term. Washington, he wrote, “must test new nuclear weapons for reliability and safety in the real world for the first time since 1992.” Doing so, he added, would help the United States “maintain technical and numerical superiority to the combined Chinese and Russian nuclear stockpiles.”

At the Cold War’s end, in 1992, the United States gave up the explosive testing of nuclear arms and eventually talked other atomic powers into doing likewise. The United States instead turned to experts and machines at the nation’s weapons labs to verify the lethality of the country’s arsenal. Today the machines include room-size supercomputers, the world’s most powerful X-ray machine and a system of lasers the size of a sports stadium.

In his article, Mr. O’Brien described such work as just “using computer models.” Republican members of Congress and some nuclear experts have faulted the nonexplosive testing as insufficient to assure the U.S. military establishment that its arsenal works, and have called for live tests.

But the Biden administration and other Democrats warn that a U.S. test could lead to a chain reaction of testing by other countries. Over time, they add, resumption could result in a nuclear arms race that destabilizes the global balance of terror and heightens the risk of war.

“It’s a terrible idea,” said Ernest J. Moniz, who oversaw the U.S. nuclear arsenal as the secretary of energy in the Obama administration. “New testing would make us less secure. You can’t divorce it from the global repercussions.”