The plot thickens. Berg, who barely spoke a word of Arabic, was hauling around a Farsi prayer book. Why????
My theory: it's a "physical password" or proof of bona fides. Iranian contact A says, "go here and meet Big Abdul, give him this book. He'll take you to who you need to meet."
Contact A underlines certain lines in the book, a very low-level "prayer code." The underlined or tic marked passage says to Big Abdul, "trust this infidel, pass him up the chain."
Or, it means, "This stupid American Jew could be useful. Do with him what you want."
I hadn't picked up on his mention of Iran being pertinent to his stay. I think you are onto something with your post.
As a reader of spy novels, which sort of lost their allure after the end of the Cold War but have regained popularity after 9/11, that book would serve exactly the purpose you proposed.
Maybe he couldn't find a copy of "Catcher in the Rye" at the Baghdad Barnes & Noble. :-)