At a hearing last week, Scott Boughton, an assistant attorney general for the state, said the measure was not intended to infringe on anyone’s religion; it was intended to keep Oklahoma judges from looking at the legal principles of other nations and cultures in applying state and federal law. When the judge asked whether that had ever happened in Oklahoma, however, Mr. Boughton acknowledged that he did not know of an instance in which Shariah law had been invoked by the courts.

Mr. Awad testified in court that the amendment was impossible to enforce, since the concept of Shariah law varies from person to person. He asserted the law might make it impossible for the courts to enforce his own last will and testament, since it requests he be buried according to Islamic principles.

Many Muslims in Oklahoma worry the courts will no longer be able to adjudicate Islamic marriages, wills and contracts.

In her ruling on Monday, Judge Miles-LaGrange said she agreed with Mr. Awad’s contention that the definition of Shariah shifts depending on the country in which a Muslim lives and on each person’s religious beliefs.

She noted that one strong precept of Islamic law is to abide by the law of one’s land, and this explains why American Muslims do not generally practice bigamy, even though the Koran allows it.

The judge concluded that Shariah law “lacks a legal character” and “is not ‘law’ but is religious traditions that differ among Muslims.” As a result, she said, the amendment “conveys a message of disapproval of plaintiff’s faith and, consequently, has the effect of inhibiting plaintiff’s religion.”

Supporters of the measure in the state Legislature had portrayed it as a protection against what they see as an international effort by radical Muslims to establish Islamic law throughout the world.