Who can identify the true nature of any religion? It's a question that's been addressed about Islam with particular urgency in the past year by people in and outside that faith. Muslims in the United States and around the world have offered a spectrum of answers. Non-Muslims such as President Bush and the Rev. Franklin Graham have offered their own wildly varying responses.

But it's also the question that divides the leadership in the Southern Baptist Convention. It's the question raised by the "confessing movement" of the United Methodist Church. It's the center of the debate in Israel over the definition of who is Jewish. And it's a challenge raised by some of the laity movements in the Catholic Church.

Today's multifaith controversy over the nature of Islam is only the latest in a long dialogue, with Christianity offering a redefinition of Judaism, Islam challenging the sacred texts of Christians and Jews, the Church of Jesus Christ of Latter-day Saints discerning errors in other faiths, and so on.

But the question about Islam is now far more than a theological argument, say some contenders in the debate. It's a matter of international security. Or it's a challenge to civil rights. Is Islam a religion of peace, as Bush has said repeatedly? Or is it a violent scam, as the Rev. Pat Robertson said recently on the Fox TV show "Hannity and Colmes"? Where can anyone go for a definitive answer to questions about whether a particular behavior is or is not true to Islam?

There is no single answer, said Imam Yusuf Kavakci, head of the Dallas Central Mosque in Richardson, Texas. Muslim history has had a hierarchy of scholars and political leaders, starting with Muhammad himself. But unified authority was lost with the end of the Ottoman Empire in 1920, the disintegration of the Muslim world into many nations, and the presence of Muslims as a growing minority of many other countries, Imam Kavakci said.

That means that when Osama bin Laden and his followers -- or other groups -- claim to act in the name of Islam, there is no universally recognized authority that can say without contradiction that they're wrong, he said. Individual, respected scholars in Muslim nations and the United States can and have issued denunciations. But there is no single forum where consensus can be reached, he said.

"It's a problem we Muslims have," he said.

It's not just a problem for Muslims, said Robert Spencer, author of one of several recent books by non-Muslims that seek to critique that faith. Spencer claims no credential beyond 20 years of his own study of Islam. The thesis of his book, "Islam Unveiled," is that Muslim texts and history show that there is no single authority that can define the true nature of modern Islam as a religion of peace.

Judaism and Protestant Christianity have the same problem of not having a recognized single authority that can decide difficult questions of interpretation, said Spencer, who lives in New Hampshire.

"That's one reason I'm a Catholic," he said.

Like other non-Muslim critics of Islam, including the authors of a book titled "Unveiling Islam," Spencer pulls verses from the Quran and the collected sayings of Muhammad called hadiths to bolster his claims that Islam has a violent core.

"Unveiling Islam" was written by brothers who converted to Christianity from Islam while in their teens. Ergun Caner is now a professor at Criswell College in Dallas. Emir Caner is a professor at Southeastern Baptist Theological Seminary in North Carolina.

Ergun Caner said he does not hold himself or his book up as the last word on Islam. He acknowledges that some Muslims will challenge his ability to understand their faith because he does not understand the 1,400-year-old Arabic of the Quran. But he said that he has read many modern Arabic commentaries -- for and against Islam -- and that his interpretation cannot be dismissed with a blanket statement that Islam is a religion of peace.

"Islam doesn't speak with one voice, and neither does Christianity," he said.

Some of the more radical voices claiming to speak for Islam are doctors and engineers, not Muslim legal scholars whose ignorance of Muslim history has led to impossible interpretations of the Quran, he said.

So how can people hope to separate the essence from the heretical? "The answer is political in both the best and worst sense of that word," said the Rev. George Mason, a nationally recognized moderate Baptist leader.