While the deal was opposed by all Republicans in the House and Senate, it is not clear that Mr. Trump would move quickly to renege on it. Any effort by the United States to walk away from its terms, or to renegotiate it, would open the way for Iran to insist on changes as well.

The agreement has been controversial in Iran, where clerics and opponents and President Hassan Rouhani have argued that the promised economic benefits have come far too slowly. Mr. Rouhani is facing an election in coming months, and if Mr. Trump dismantled the deal, it could give his hard-line opponents an argument in favor of ousting his government.

Moreover, Mr. Trump’s nominee for defense secretary, James N. Mattis, is likely to counsel against abandoning the deal, according to officials who have discussed it with him. It is unclear what Rex W. Tillerson, the chief executive of Exxon Mobil and the nominee for secretary of state, would advise.

Mr. Trump’s choice for national security adviser, Michael T. Flynn, the retired head of the Defense Intelligence Agency, has been a major critic of the deal. In June 2015, just before the final agreement was struck, he told a congressional committee that Iran was almost certainly hiding facilities.

In Monday’s letter, the scientists and nuclear experts noted that the accord takes no options off the table for Mr. Trump or any future president. “It makes it much easier for you to know if and when Iran heads for a bomb,” they wrote. “It provides both time and legitimacy for an effective response.”

Many of the 37 signatories were among the 29 who praised the accord in a letter to President Obama in August 2015, a month after the deal was signed and sharp public debate had begun on its merits.