The Iran nuclear accord, assailed by President Trump and his revamped retinue of advisers, received a strong endorsement Monday from a bipartisan group of more than 100 national security veterans, who said the United States gains nothing by scrapping it.

The group, including 50 retired military officers and at least four former American ambassadors to Israel, added its voice to a fractious debate over the accord, which Mr. Trump has called “the worst deal” ever.

In a statement, the group, which calls itself the National Coalition to Prevent an Iranian Nuclear Weapon, enumerated 10 reasons that, in its view, preserving the accord is in the best interests of the United States.

They included the determination by United Nations inspectors that the accord is working; the importance of preserving close relations with major European allies, which all support the accord; and the possibility of reaching a nuclear agreement with North Korea, which might not negotiate if it believes that the United States abrogates international pledges.