The Brooklyn Public Library has agreed to stock a book that refers to London as a hotbed of terrorism, as an acquisitions librarian who initially rejected a patron’s suggestion to buy the book, calling it “potentially incendiary,” reversed his decision.

The librarian, Wayne Roylance, changed his mind days after the patron, disappointed with the decision, emailed him prominent critics’ appraisals of the book, “Londonistan” by Melanie Phillips, a library spokeswoman said.

The 2006 book blames extreme multiculturalism for making the city what it calls a jihad Petri dish that produces attacks such as a transit bombing last July that killed 52 commuters. The library’s spokeswoman, Stefanie Arch, defended the decisions leading to the “Londonistan” acquisition, noting that the library’s procedures eventually worked, as the book was ordered.

“He misspoke when he used that term,” Ms. Arch said, referring to the “potentially incendiary” characterization, “and he apologized.”

The library declined to make Mr. Roylance available for an interview, and the patron who requested “Londonistan” didn’t answer a call placed last night to a number listed in his name. Civil libertarians say public libraries should offer diversity. “As we have said time and time again, excluding a viewpoint or topic from the shelves because it’s unpopular, incendiary, or for other reasons is not the best way to ensure the free marketplace of ideas,” the New York Civil Liberties Union’s executive director, Donna Lieberman, said.

She said libraries should have general, established criteria for selecting books. The Brooklyn Public Library’s policy lists 14, including that potential acquisitions have the attention of critics and reviewers.