SAN FRANCISCO - A federal appeals court in San Francisco refused Monday to let Arizona require its police to demand documentation from suspected illegal immigrants, saying the state is intruding into federal authority and harming U.S. foreign policy.

Shane Oanes (front, right), 24 years old, from San Francisco, and Josephine Saechao (yellow sign), 17 years old, from Richmond attend a rally on Mission at 24th streets in reaction to the Arizona immigration law which went into effect today in San Francisco, Calif., on Thursday, July 29, 2010. (Liz Hafalia / The Chronicle) In a 2-1 ruling, the Ninth U.S. Circuit Court of Appeals upheld a federal judge's decision blocking major provisions of a law that sought to inject the state into immigration enforcement. The Obama administration had sued to strike down the law.

State officials indicated they would appeal.

Arizona, which in recent years has seen the nation's greatest influx of illegal immigrants, argued that the federal government had failed to police borders and needed new forms of state assistance, despite record levels of deportations under President Obama. Conservative legislators in other states, including California, have drafted similar measures.

The centerpiece of the April 2010 Arizona law is a requirement that police demand proof of legal status from anyone in their custody whom they reasonably suspect of being in the country illegally.

Citing a federal law that allows states to provide information to immigration officials, Arizona said its law would require police only to make reasonable efforts to determine a person's immigration status and would not interfere with federal enforcement.

But the court majority said the state law goes further and requires police who arrest suspects to verify their immigration status with federal authorities before releasing them. The court said that mandate, which applies to those who are arrested and not merely detained, turns police into immigration officers.

The law "interferes with the federal government's authority to implement its priorities and strategies in law enforcement," Judge Richard Paez said in the majority opinion.

He said states can enforce immigration restrictions only with federal officials' advance consent and under their supervision.

Paez also said the Arizona law has harmed U.S. foreign relations. He cited protests from the U.N. secretary-general and numerous Latin American nations, notably Mexico, which has limited its participation in a border conference and delayed a proposed agreement on responding to national disasters.

Judge John Noonan sided with Paez and wrote a separate opinion stressing the need for a uniform immigration policy.

"That 50 individual states or one individual state should have a foreign policy is absurdity," Noonan said.

Dissenting Judge Carlos Bea said the Obama administration, not Arizona, is responsible for any disruption of U.S. immigration policy.

"The executive's desire to appease foreign governments' complaints cannot override congressionally mandated provisions" to let states help enforce immigration law, he said.

The state law would intrude on federal authority, Bea said, only if administration officials "do not want to enforce the immigration laws."

The court also blocked provisions that would make it a crime to be in Arizona illegally or to fail to carry immigration documents. It rejected enforcement of other sections allowing police to detain anyone they believe is deportable because of a crime in another state, and making it a crime for an illegal immigrant to hold a job or seek employment.

Arizona Gov. Jan Brewer said she would confer with state lawyers on whether to ask the full appeals court for a rehearing or appeal directly to the U.S. Supreme Court.

The ruling "does harm to the safety and well-being of Arizonans who suffer the negative effects of illegal immigration," Brewer said.

Online: The ruling can be read at links.sfgate.com/ZKYA.