The ruling marked a repudiation of the Arizona law as U.S. District Judge Susan Bolton indicated that the government has a good chance at succeeding in its argument that federal immigration law trumps state law. It was an important first-round victory for the government in a fight that may not be settled until the U.S. Supreme Court weighs in.

But opponents of the law said the ruling sends a strong message to other states hoping to replicate the law. "Surely it's going to make states pause and consider how they're drafting legislation and how it fits in a constitutional framework," Dennis Burke, the U.S. Attorney for Arizona, told reporters. "The proponents of this went into court saying there was no question that this was constitutional, and now you have a federal judge who's said 'hold on, there's major issues with this bill.'"

He added: "So this idea that this is going to be a blueprint for other states is seriously in doubt. The blueprint is constitutionally flawed."

Gov. Jan Brewer called Wednesday's decision "a bump in the road" and vowed to appeal. The key sponsor of Arizona's law, Republican Rep. Russell Pearce, said the judge was wrong and predicted that the state would ultimately win the case.

Her spokesman Paul Senseman said the state would ask the 9th U.S. Circuit Court of Appeals in San Francisco on Thurdsay to lift Bolton's preliminary injunction and to expedite its consideration of the state's appeal.

The key sponsor of Arizona's law, Republican Rep. Russell Pearce, said the judge was wrong and predicted that the state would ultimately win the case.

In her temporary injunction, Bolton delayed the most contentious provisions of the law, including a section that required officers to check a person's immigration status while enforcing other laws. She also barred enforcement of parts requiring immigrants to carry their papers and banned illegal immigrants from soliciting employment in public places - a move aimed at day laborers that congregate in large numbers in parking lots across Arizona. The judge also blocked officers from making warrantless arrests of suspected illegal immigrants.

"Requiring Arizona law enforcement officials and agencies to determine the immigration status of every person who is arrested burdens lawfully present aliens because their liberty will be restricted while their status is checked," said Bolton, a Clinton appointee who was assigned the seven lawsuits filed against Arizona over the law.

Other provisions that were less contentious were allowed to take effect yesterday morning, including a section that bars cities in Arizona from disregarding federal immigration laws.

The 11th-hour ruling came just as police were preparing to begin enforcement of a law that has drawn international attention and revived the national immigration debate in a year when Democrats are struggling to hold on to seats in Congress.

The ruling was anxiously awaited in the U.S. and beyond. About 100 protesters in Mexico City who had gathered in front of the U.S. Embassy broke into applause when they learned of the ruling. They had been monitoring the news on a laptop computer. Mariana Rivera, a 36-year-old from Zacatecas, Mexico who is living in Phoenix on a work permit, said she heard the news live on a Spanish-language news program.