Iran's 1979 revolution overthrew the Shah, whom Muslim revolutionaries denounced as a "U.S. puppet" installed by the CIA. There was little U.S. public understanding of the CIA's role in the 1953 overthrow of a democratically elected Iranian leader and the resultant widespread Iranian public anger toward the U.S.
"When we saw people shouting 'Death to America' ... we had no context to put that in," Esposito said.
U.S. political and cultural leaders also help shape public attitudes.
After Sept. 11, President George W. Bush took great pains to distinguish between Islam in general and terrorists who are Muslim. Initially, polls found the U.S. public made that distinction. A Pew survey soon after Sept. 11 asked whether Islam encourages violence more than other faiths, and Americans were twice as likely to say no than yes. Within a couple of years, however, that distinction was gone. Most Americans thought that Islam did encourage violence more.
"Events are filtered through the media and the reaction by others" as well as people's pre-existing views, said Alan Cooperman, of the Pew Forum on Religion & Public Life.
Public leaders' reactions to the planned Islamic cultural center two blocks from the World Trade Center site offer the latest example.
Mayor Michael Bloomberg and President Barack Obama supported the project's developers' right to proceed, and Obama spoke out against religious discrimination. However, the president sent a mixed message when he said the next day that he wasn't commenting on the wisdom of the project's location - a neighborhood filled with bars, restaurants, a strip club and an off-track betting parlor.
The outspoken opposition of prominent Republicans - including Newt Gingrich and Sarah Palin - connects the Sept. 11 attacks to Islam. The issue could become divisive in some elections this November.
The Internet and social networking applications have bypassed the traditional media filter and magnified the influence of fringe activists on public perceptions of Islam.
Ihsan Bagby, an associate professor of Islamic studies at the University of Kentucky, said conservative Christians long have been a source of anti-Islamic rhetoric, but more secular voices are now in the mix. Bagby cited Pam Geller, a blogger who's warned of "Islamization" of America and is a strident opponent of the New York Islamic cultural center. Bagby said that Americans' long-held suspicions of Muslims are "made more virulent by these groups."
Anti-Muslim feelings aren't likely to decline substantially until American attitudes improve toward the religion itself, said Dalia Mogahed, the executive director of the Gallup Center for Muslim Studies.
Muslims are the most negatively viewed faith community in the country, Gallup found. However, Pew polling finds that Americans also think that Muslims face the most discrimination of any U.S. religious group, which could imply a sense of sympathy.
There are modest indications that Americans are becoming more familiar with Islam even if they don't think they are, and that this may continue as the U.S. Muslim population grows. For years, Pew has asked Americans whether they know Muslims' name for God and their equivalent of the Bible. The percentage of Americans familiar with Allah and the Quran was 33 percent in 2002, but 41 percent by last year. Still, Islam's favorability has declined.
Pew's Cooperman said that when polling is considered overall, "I just could not make a case that in general U.S. public opinion has either hardened or softened" toward Muslims.
Still, U.S. history offers some hope for positive change. Catholics and Jews once experienced severe discrimination that's ebbed with time. So have U.S. ethnic minorities persecuted during eras of war with their homelands - consider the internment of Japanese-Americans and the persecution of German-Americans in the 20th century.
