The first signature on the letter is from Richard L. Garwin, a physicist who helped design the world’s first hydrogen bomb and has long advised Washington on nuclear weapons and arms control. He is among the last living physicists who helped usher in the nuclear age.

Also signing is Siegfried S. Hecker, a Stanford professor who, from 1986 to 1997, directed the Los Alamos weapons laboratory in New Mexico, the birthplace of the bomb. The facility produced designs for most of the arms now in the nation’s nuclear arsenal.

Other prominent signatories include Freeman Dyson of Princeton, Sidney Drell of Stanford and Rush D. Holt, a physicist and former member of Congress who now leads the American Association for the Advancement of Science, the world’s largest general scientific society.

Most of the 29 who signed the letter are physicists, and many of them have held what the government calls Q clearances — granting access to a special category of secret information that bears on the design of nuclear arms and is considered equivalent to the military’s top secret security clearance.