From [HERE] PHOENIX — The United States Court of Appeals for the Ninth Circuit ruled against the State of Arizona on Monday and let stand a lower court decision blocking the most contentious parts of the state’s immigration law from going into effect.

The decision calling the provisions unconstitutional was a victory for the Obama administration, which argued that the law interfered with the federal government’s authority over immigration. Two judges ruled against Arizona, and one dissented in part from them.

The law would have required the police to question people about their immigration status if they had been stopped for other matters and if the officers found reasonable suspicion that they were illegal immigrants. Critics said that was an invitation to racial profiling.

Also challenged were provisions requiring immigrants to carry their papers and making it a violation for illegal immigrants to work or look for work.

Last July, just days before the law was to take effect, Judge Susan Bolton of Federal District Court issued an injunction blocking parts of it. Gov. Jan Brewer, a Republican who supports the crackdown on immigrants, filed an appeal seeking to have the injunction lifted.

After the appeals court rejected the state’s request on Monday and issued a lengthy decision indicating that it believed the state had overstepped its authority, State Senator Russell K. Pearce, a Republican who is the principal sponsor of the law, remained defiant, saying the issue would ultimately be decided by the Supreme Court.

“This battle is a battle of epic proportions,” Mr. Pearce said in a statement suggesting he was not surprised by the ruling. “It is about a state’s right to enforce the laws of this land and protect its citizens from those who break our laws.”

Ms. Brewer and the Arizona attorney general, Tom Horne, also vowed to keep fighting for the law. “I believe the Ninth Circuit decision will be overturned by the United States Supreme Court, and I pledge to make every possible effort to achieve that result,” Mr. Horne said.

Critics of the law, who have held protests and filed lawsuits to strike it down, were thrilled with the ruling.

“One of the reasons we have a judiciary is so that mobs don’t rule, so that when the Legislature oversteps its bounds there is someone to stop them,” said Omar Jadwat of the A.C.L.U. Immigrants’ Rights Project.

It was not immediately clear how the state would proceed. It could appeal the decision to the full Ninth Circuit, or it could immediately appeal to the Supreme Court. The state could also hold off on appealing and return to the Federal District Court in Phoenix, where Judge Bolton continues to oversee challenges to the law.

“In upholding Judge Bolton’s decision, the Ninth Circuit has signaled, in a loud and clear voice, that Arizona’s effort to regulate immigration law and policy directly violates the Constitution and will not stand,” said David Leopold, president of the American Immigration Lawyers Association.

The decision will be closely watched in several states that are considering similar laws of their own. The Georgia Senate was set to debate the matter on Monday, and another bill appeared on the move in Alabama.

Other states, including Mississippi and Kansas, watered down or abandoned tough bills to avoid the litigation and protests that Arizona faced. After lawmakers in Utah concluded that the administration’s challenge to Arizona was likely to prevail, they took a different tack. They voted for a milder enforcement bill, but also voted to create a guest worker program for illegal immigrants.

Backers of the Arizona law said they were pleased with disagreements among the appeals court judges. Judge Carlos Bea issued a partial dissent in which he criticized the majority’s argument by quoting from Lewis Carroll’s “Alice in Wonderland.”