The Simon Wiesenthal Center, which has been tracking hate Web sites for nine years, describes in the report released Monday more than 200 of about 4,000 online hate sites it monitors.
The group said it has seen a surge this year in the number of sites that promote terrorist recruitment, urging young people to join "holy wars" and become suicide bombers.
The report includes sites that deny the Holocaust, theorize Sept. 11 conspiracies and glorify al Qaeda. The more common hate sites features racism, anti-Semitism and gay bashing.
"People need to realize how much hatred there is ... and the extraordinary technological advance of people who are spreading these lies," said New York City Council Speaker Gifford Miller, who attended the news conference where the report was released.
Some of the most troubling, he said, are sites that appear to be educational, like a Web site on black civil rights leader Martin Luther King Jr. that is actually run by a racist organization. Such sites could fool schoolchildren doing research, Miller said.
The Simon Wiesenthal Center uses the report to help inform parents, teachers, public officials and law enforcement.
The intent is not to interfere with free speech and shut down the sites, said Mark Weitzman, director of the center's Task Force Against Hate. "This is for public awareness," he said.