“At a moment like this it’s important for the public that’s weighing out these different cases and policies to recognize the breadth of concern,” said Suzanne Nossel, the executive director of PEN America, which wrote the letter and plans to spread it on social media.

The letter noted how the original visa ban last month had disrupted cultural life. The Iranian director Asghar Farhadi, whose film “The Salesman” is up for a foreign-language Academy Award, said he would not attend this weekend’s Oscars ceremony. It said the Syrian singer Omar Souleyman might not be able to perform in New York in May, and it was unclear whether the Paris-based Syrian poet Adonis, who is 87, would be able to attend PEN’s World Voices Festival in New York in May. That literary festival was founded by Salman Rushdie to foster literary conversation across borders and promote free expression.

George Packer, the author and staff writer for The New Yorker, said he was under no illusions about the efficacy of signing his name to a letter like this. “I don’t expect it to change any minds at the top of the Trump administration, but perhaps it will give heart to officials lower down, and to foreigners who wonder if America is losing what makes it great,” he said.

“I’ve had enough refugees from banned countries staying in my own house to know that they’re exactly the kind of people we should welcome,” Mr. Packer added. “America’s openness to foreigners has earned us affection and respect around the world even in dark times. Why throw it away?”

The novelist Rick Moody said he hoped the letter would help in “keeping the resistance alive.” “Or, ideally,” he added, “budging the needle on policy a bit.” And the writer Susan Orlean echoed that sentiment: “I think this is the time to be noisy — to be loud about disagreeing when it comes to matters of essential unfairness.”