Alarmed that President Trump may soon take steps that could unravel the international nuclear agreement with Iran, more than 80 disarmament experts urged him on Wednesday to reconsider and said the accord was working.

In a joint statement, the experts said the 2015 agreement, negotiated by the Obama administration and the governments of Britain, China, France, Germany and Russia, was a “net plus for international nuclear nonproliferation efforts.”

Because of the monitoring powers contained in the agreement, they said, Iran’s capability to produce nuclear weapons has been sharply reduced. They also said the agreement made it “very likely that any possible future effort by Iran to pursue nuclear weapons, even a clandestine program, would be detected promptly.”

Mr. Trump has repeatedly assailed the agreement — a signature achievement of his predecessor — describing it as “a terrible deal” and a giveaway to Iran.