A federal appellate court on Monday upheld a judge's ban on the most controversial parts of a new Arizona immigration law, setting the stage for a showdown at the U.S. Supreme Court over how far a state can go to expel illegal immigrants.

The three-judge panel of the 9th U.S. Circuit Court of Appeals agreed with a federal judge in Arizona who found that some provisions of the law were an unconstitutional intrusion into immigration and foreign policy, which are the prerogatives of the federal government. The law was signed last year by Gov. Jan Brewer, who argued that her state was overrun by dangerous illegal immigrants. Critics said it would lead to racial profiling.

In a partial dissent, one judge argued that one provision of the law, which requires police to determine the status of people they stop and think are in the country illegally, was constitutional. But that position did not sway the other two judges

The ruling was a victory for the Obama administration, which challenged Arizona's law in court last year.

Brewer and Arizona Attorney General Tom Horne issued a joint statement criticizing the ruling. They did not say, however, whether they would appeal it to a full panel of the 9th Circuit or straight to the Supreme Court. The top court is considering a challenge to another Arizona law that dissolves businesses that repeatedly hire illegal immigrants.

"I remain steadfast in my belief that Arizona and other states have a sovereign right and obligation to protect their citizens and enforce immigration law in accordance with federal statute," Brewer said.

Civil rights groups and immigration advocates were jubilant. "We're really glad to see the side of civil rights and the constitution have prevailed," said Lydia Guzman of Phoenix, who helped organize protests of the law before it was largely suspended in July.

All the judges — two appointed by Republican presidents and one by a Democrat — agreed that the state went too far in making it a crime to lack immigration papers in Arizona or to work there while being in the country illegally. They agreed that Congress and the courts have historically reserved the ability to penalize illegal immigrants for the federal government.

Judge Richard Paez, who was appointed by President Bill Clinton and wrote the majority opinion, argued that requiring police to perform immigration enforcement makes it impossible for the federal government to regulate immigration. "By imposing mandatory obligations on state and local officers, Arizona interferes with the federal government's authority to implement its priorities and strategies in law enforcement, turning Arizona officers into state-directed immigration agents," Paez wrote.

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Judge Richard T. Noonan, an appointee of President Ronald Reagan, wrote a separate concurring opinion emphasizing that Arizona had clearly tried to create its own immigration — and therefore, foreign — policy. He noted that a number of countries protested the law, which begins by stating that "attrition through enforcement" is now the state's policy.

"It would be difficult to set out more explicitly the policy of a state in regard to aliens unlawfully present," Noonan wrote. "Without qualification, Arizona establishes its policy on immigration."