WASHINGTON — An atheist told the Supreme Court today that the words "under God" in the Pledge of Allegiance are unconstitutional and offensive to people who don't believe there is a God.

Michael Newdow, who, on behalf of his daughter, challenged the pledge of loyalty to the country usually recited in American classrooms, said the Court has no choice but to keep it out of public schools.

"It's indoctrinating children," he said. "The government is supposed to stay out of religion."

But some justices hearing the case, Elk Grove Unified School Dist. v. Newdow, said they were not sure if the words were intended to unite the country or express religion.

Chief Justice William H. Rehnquist noted that Congress unanimously added the words "under God" in the pledge in 1954.

"That doesn't sound divisive," he said.

"That's only because no atheists can be elected to office," Newdow responded.

Some in the courtroom audience erupted in applause, and were threatened with expulsion by the chief justice.

The subject of Newdow's right to bring the lawsuit had dominated the beginning of arguments in the landmark case to decide if the classroom salute in public schools violates the Constitution's ban on government-established religion.

Terence Cassidy, attorney for the suburban Sacramento school district where Newdow's 9-year-old daughter attends classes, told justices that the girl's mother opposed the lawsuit. "The ultimate decision-making authority is with the mother," he said.

Newdow had sued the school and won, setting up the landmark appeal before a court that has repeatedly barred school-sponsored prayer from classrooms, playing fields and school ceremonies. But justices could dodge the issue altogether if they decide that Newdow needed the mother's consent because she has primary custody.

"He says 'I have my own rights, I have a right as a father to try to influence this child,'" Justice Anthony M. Kennedy said.

Rehnquist said that the issues raised in the case "certainly have nothing to do with domestic relations." Justice David H. Souter said Newdow could argue that his interest in his child "is enough to give him personal standing."

Even though a state judge said Newdow's daughter could not attend the oral arguments, some of the justices seemed worried about the eventual impact on her.

Justice Kennedy told Newdow that he was asking the Court to "exercise the extraordinary, the breathtaking power to declare federal law unconstitutional."

"It seems to me that your daughter is the one that bears the blame for this. She's going to face the public outcry, the public outrage," Kennedy said.

Newdow said he was not worried about adverse consequences for the girl, who has not been named in court records.

"My daughter's going to be able to walk around and say that 'my father helped uphold the Constitution of the United States,'" he responded.

Absent from the case is one of the Court's most conservative members, Justice Antonin Scalia, who bowed out after he criticized the 9th U.S. Circuit Court of Appeals ruling in Newdow's favor during a religious rally last year. Newdow had requested his recusal.

Solicitor General Theodore Olson, the Bush administration lawyer arguing for the school district, said that the mother was concerned that her daughter had been "thrust into the vortex of this constitutional case."

He said the Pledge of Allegiance should be upheld as a "ceremonial, patriotic exercise."

A new poll shows that Americans overwhelmingly support the reference to God. Almost nine in 10 people said the reference to God belongs in the pledge despite constitutional questions about the separation of church and state, according to an Associated Press poll.

Dozens of people camped outside the court on a cold night, bundled in layers of clothing and blankets, to be among the first in line to hear the historic case. More than 100 supporters of the pledge began the day reciting the pledge and emphasizing the words "under God."

"After today, this Court will decide whether America remains one nation under God or whether we shake a fist in God's face," the Rev. Rob Schenck, president of the National Clergy Council, told a crowd of people carrying signs that read: "I support the pledge."

Some supporters of Newdow, outnumbered about four-to-one, shouted over the speeches of pledge proponents. They carried signs with slogans like "Democracy Not Theocracy."

The phrase "under God" was not part of the original pledge written in 1892. Congress inserted it in 1954, after lobbying by religious leaders during the Cold War. Since then, it has become a familiar part of life for generations of students.

Newdow compared the controversy to the issue of segregation in schools, which the Supreme Court took up 50 years ago.

"Aren't we a better nation because we got rid of that stuff?" Newdow, a 50-year-old lawyer and doctor arguing his own case at the Court, asked before the argument.

The AP poll, conducted by Ipsos-Public Affairs, found college graduates were more likely than those who did not have a college degree to say the phrase "under God" should be removed. Democrats and independents were more likely than Republicans to think the phrase should be taken out.

Justices have been urged to throw out the case, without a ruling on the constitutional issue, because of questions about whether Newdow had custody of his daughter when he filed the suit.

The girl's mother, Sandra Banning, is a born-again Christian and supporter of the pledge.

"I object to his inclusion of our daughter" in the case, Banning said today on ABC television. She said she worries that her daughter will be "the child who is remembered as the little girl who changed the Pledge of Allegiance."

Newdow told the Court that his daughter was not an atheist, but that justices should consider her views as a developing young person.

"Imagine you're this one child with a class full of theists and you have this idea that you want to perhaps at least consider and you have everyone imposing their view on you," he said.

"There's a principle here and I'm hoping the Court will uphold this principle so that we can finally go back and have every American want to stand up, face the flag, place their hand over their heart and pledge to one nation, indivisible, not divided by religion, with liberty and justice for all."