Now nine influential American Muslim scholars have come together in a YouTube video to repudiate the militants' message. The nine represent a diversity of theological schools within Islam, and several of them have large followings among American Muslim youths.

The video is one indication that American Muslim leaders are increasingly engaging the war of ideas being waged within Islam.

"We need to shepherd our own flock and to say that, theologically, these things are unacceptable," said Imam Suhaib Webb, the educational director for the Muslim American Society, a grass-roots group in Santa Clara, Calif., who is among the nine in the video. "The Prophet Muhammad, when on the battlefield, saw that amongst the enemy there were innocent women and children killed, and he was openly angry. He is prohibiting us from killing the innocent. It is very clear."

Mr. Webb said in an interview on Friday that as a white convert from Oklahoma, he had become deeply alarmed in the past year at the number of converts who had been arrested on charges of planning or carrying out violence in the name of Islam.