While proponents of the legislation have seized on aspects of Shariah that are unfavorable to women, Mr. Yerushalmi’s focus is broader. His interest in Islamic law began with the Sept. 11 attacks, he said, when he was living in Ma’ale Adumim, a large Jewish settlement in the Israeli-occupied West Bank.

At the time, Mr. Yerushalmi, a native of South Florida, divided his energies between a commercial litigation practice in the United States and a conservative research institute based in Jerusalem, where he worked to promote free-market reform in Israel.

After moving to Brooklyn the following year, Mr. Yerushalmi said he began studying Arabic and Shariah under two Islamic scholars, whom he declined to name. He said his research made clear that militants had not “perverted” Islamic law, but were following an authoritative doctrine that sought global hegemony — a mission, he says, that is shared by Muslims around the world. To illustrate that point, Mr. Yerushalmi cites studies in which large percentages of Muslims overseas say they support Islamic rule.

In interviews, Islamic scholars disputed Mr. Yerushalmi’s claims. Although Islam, like some other faiths, aspires to be the world’s reigning religion, they said, the method for carrying out that goal, or even its relevance in everyday life, remains a far more complex subject than Mr. Yerushalmi suggests.

“Even in Muslim-majority countries, there is a huge debate about what it means to apply Islamic law in the modern world,” said Andrew F. March, an associate professor specializing in Islamic law at Yale University. The deeper flaw in Mr. Yerushalmi’s argument, Mr. March said, is that he characterizes the majority of Muslims who practice some version of Shariah — whether through prayer, charitable giving or other common rituals — as automatic adherents to Islam’s medieval rules of war and political domination.

It is not the first time Mr. Yerushalmi has engaged in polemics. In a 2006 essay, he wrote that “most of the fundamental differences between the races are genetic,” and asked why “people find it so difficult to confront the facts that some races perform better in sports, some better in mathematical problem-solving, some better in language, some better in Western societies and some better in tribal ones?” He has also railed against what he sees as a politically correct culture that avoids open discussion of why “the founding fathers did not give women or black slaves the right to vote.”

On its Web site, the Anti-Defamation League, a prominent Jewish civil rights organization, describes Mr. Yerushalmi as having a record of “anti-Muslim, anti-immigrant and anti-black bigotry.” His legal clients have also drawn notoriety, among them Pamela Geller, an incendiary blogger who helped drive the fight against the Islamic community center and mosque near ground zero.