For years, Olga Paule Perrier-Bilbo, a French national and green-card holder who has lived in Scituate since 2000, has wanted to become an American citizen.

That dream, she claims in a new federal lawsuit, is being denied by four simple words: "So help me God."

On Thursday, Perrier-Bilbo, an atheist, filed a federal lawsuit claiming the inclusion of that phrase in United States' citizenship oath is an unconstitutional violation of her religious freedom.

"Accordingly, the current oath violates the first 10 words of the Bill of Rights, and to participate in a ceremony which violates that key portion of the United States Constitution is not supporting of defending the constitution as the oath demands," the lawsuit says.

And although Perrier-Bilbo was offered the chance to use a modified oath or participate in a private citizenship ceremony, she claims the presence of "so help me God" is still an unconstitutional government endorsement of religion -- and that the alternatives offered to her by the government place an illegal burden on her for her beliefs.

"By placing a religious statement (to which Plaintiff does not adhere) into the Oath of Naturalization, and then forcing Plaintiff to use an alternative oath (so that she must feel less than a new citizen), Defendants substantially burden Plaintiff in her exercise of religion," the suit claims.

The First Amendment's clauses regarding freedom of religion -- which say that Congress "shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof" -- have been the subject of dozens of Supreme Court cases, with states, federal agencies and private citizens sparring over the proper relationship between religion and government.

In the 20th century, the court handed down a number of rulings both protecting religious people from laws that disadvantaged them and banning government agencies from endorsing or imposing religion.

Three rulings in the early 1960s barred mandatory prayer and bible readings at public schools. A 1968 ruling overturned an Arkansas law banning the teaching of evolution. Amish people gained the right to withdraw their children from public schools; a nativity scene in a town square was declared constitutional, while one placed in a courthouse was banned as a religious message.

Atheists and civil liberties organizations have continued to bring cases challenging alleged government endorsements of religion. In their most recent Supreme Court victory, two plaques bearing the Ten Commandments were ordered removed from a courthouse in Kentucky following the court's 2005 decision in McCreary County v. ACLU.

But the court has also ruled in favor of governments and religious advocates. In 2000, Michael Newdow sued his child's school district to remove the words "under God" from the Pledge of Allegiance, saying the recital of the pledge violated the Establishment Clause.

But the Supreme Court ruled he did not have standing to sue, and a federal appeals court later ruled that a teacher leading students in the pledge did not violate the First Amendment.

Newdow has also filed unsuccessful lawsuits to remove the phrase "In God We Trust" from American currency and prevent "So help me God" from being included in the Presidential oath of office.

Newdow's defeat in the Pledge of Allegiance case could signal a difficult road ahead for Bilbo's lawsuit, suggested dean of Berkeley Law Erwin Chemerinsky, an expert on the First Amendment.

"Courts generally have not been receptive to this in the context of the Pledge of Allegiance," Chemerinsky wrote in an email.

Perrier-Bilbo's suit has more in common with Newdow's pledge complaint than just its subject matter. Newdow, a California attorney, is also one of her lawyers, and was not immediately available for comment.

Perrier-Bilbo, 48, was born in Paris, France and moved to Scituate in 2000, her lawsuit says. Two years later she became a permanent resident of the U.S. and in 2004 was issued a green card.

In 2008, she began to seek citizenship, beginning a years-long series of exchanges with immigration authorities over the presence of the phrase "so help me God" in the naturalization oath.

The federal government approved her naturalization request offered to let her either participate in a citizenship ceremony without saying the phrase, or become a citizen during a private ceremony in which she could use a modified oath.

But neither were satisfactory, and on Thursday Perrier-Bilbo filed suit against Congress, the United States of America and U.S. Citizenship and Immigration Services Director L. Francis Cissna.

"The phrase 'so help me God,' added to the nation's officials Naturalization Oath, sends the ancillary message to members of the audience that disbelieve in God that they are outsiders, not full members of the political community, and an accompanying message to those that believe in God that they are insiders, favored members of the political community," the suit claims.