CHICAGO — A federal judge issued a preliminary injunction today blocking the state superintendent from enforcing a new law requiring a moment of silence in Illinois schools.

Judge Robert Gettleman's ruling came after atheist activist and talk-show host Rob Sherman filed a lawsuit against Township High School District 214 in suburban Chicago, where his daughter attends school.

Sherman, whose daughter is a freshman at Buffalo Grove High School, claims the new state law violates the U.S. Constitution. He says the injunction proves the law that went into effect last month "doesn't have a prayer."

Yesterday, Gettleman blocked the Township district from enforcing the state law, calling the statute "likely unconstitutional" and vague.

He then asked the parties in the case to return to federal court today.

Sherman's attorney, Gregory Kulis, had asked the judge yesterday to extend the injunction to the rest of the state, and Gettleman said he wanted to think about the decision overnight.

The Silent Reflection and Student Prayer Act already let schools in Illinois have a moment of silence if they desired to do so. The new law, which went into effect last month, changed the word "may" in the law to "shall," mandating a moment of silence.

The House passed the measure and sent it to Gov. Rod Blagojevich in May. The governor vetoed it in August, saying that "the separation of church and state is a centerpiece of our Constitution." The Legislature overrode his veto last month.

Gettleman said yesterday that the law could mean an endorsement of prayer, which he said was unconstitutional.

"If that's the way it's being interpreted, then I think we have a problem," he said.

The judge also said yesterday that the act was not clear enough about the definition of a "moment" and when the pause should occur.

District 214 officials have told the judge that they would enforce the law in a neutral way with a 15-second moment of silence, omitting references to religion, pending resolution of the lawsuit.

Sherman has previously filed lawsuits to remove religious symbols from the public sphere. In 1989, he filed a lawsuit challenging a state law requiring public school students to recite the Pledge of Allegiance. He said that the words "under God" contained in the pledge were unconstitutional.

The judge set the next hearing in the case for Dec. 14.