PHOENIX - Opponents of Arizona's immigration crackdown went ahead with protests Thursday despite a judge's ruling that delayed enforcement of most the law, and dozens of people in Phoenix were arrested after peacefully confronting officers in riot gear.

A protester gets arrested out on the street in front of the courthouse in Phoenix July 29, 2010. Police arrested at least 30 protesters who took to the streets of Phoenix on Thursday after Arizona adopted a new immigration law, even though its most intrusive provisions had already been blocked by a U.S. court. (REUTERS/Rick Scuteri) Gov. Jan Brewer called U.S. District Judge Susan Bolton's Wednesday's decision halting the law "a bump in the road," and her spokesman said they'd appeal to the 9th U.S. Circuit Court of Appeals in San Francisco later Thursday.

Outside the state Capitol, hundreds of protesters began marching at dawn, gathering in front of the federal courthouse where Bolton issued her ruling on Wednesday. They marched on to the office of Maricopa County Sheriff Joe Arpaio, who has made a crackdown on illegal immigration one of his signature issues.

At least eight protesters approached a police line and allowed themselves to be arrested. A group of about two dozen protesters then sat down in the middle of the street or refused to leave, and police arrested them as well.

Earlier, three people were detained at the courthouse after apparently entering a closed-off area. Former state Sen. Alfredo Gutierrez, who ran unsuccessfully for governor in 2002, was among them.

Marchers chanted "Sheriff Joe, we are here, we will not live in fear," and among the crowd was a drummer wearing a papier-mache Sheriff Joe head and dressed in prison garb.

Arpaio vowed to go ahead with a crime sweep targeting illegal immigrants. It was Phoenix police who made most the early arrests, but other protests were planned later in front of a county jail.

"My deputies will arrest them and put them in pink underwear," Arpaio said, referring to one of his odd methods of punishment for prisoners. "Count on it."

Arizona is the nation's epicenter of illegal immigration, with more than 400,000 undocumented residents. The state's border with Mexico is awash with smugglers and drugs that funnel narcotics and immigrants throughout the U.S., and supporters of the new law say the influx of illegal migrants drains vast sums of money from hospitals, education and other services.

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

"I was waiting to hear because we're all very worried about everything that's happening," said Rivera, who phoned friends and family with the news. "Even those with papers, we don't go out at night at certain times there's so much fear (of police). You can't just sit back and relax."

In New York City, about 300 immigrant advocates gathered Thursday near the federal courthouse in lower Manhattan.

New York City Councilman Jumaane Williams, a first-generation Caribbean-American, told the crowd: "We won a slight battle in Arizona, we've got to continue with the war."

In Los Angeles, about 200 protesters invaded a busy intersection west of downtown Los Angeles.

Police shut down the intersection of Wilshire Boulevard and Highland Avenue and diverted traffic away after demonstrators moved into the street and sat down at about 10 a.m. Thursday.

The protesters chanted, "These are our streets" during the raucous demonstration. Police say there have been no arrests.

Bolton indicated the government has a good chance at succeeding in its argument that federal immigration law trumps state law. But the key sponsor of Arizona's law, Republican Rep. Russell Pearce, said the judge was wrong and predicted 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 administration appointee who was assigned the seven lawsuits filed against Arizona over the law.

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

Kris Kobach, the University of Missouri-Kansas City law professor who helped write the law and train Arizona police officers in immigration law, conceded the ruling weakens the force of Arizona's efforts to crack down on illegal immigrants. He said it will likely be a year before a federal appeals court decides the case.

"It's a temporary setback," Kobach said. "The bottom line is that every lawyer in Judge Bolton's court knows this is just the first pitch in a very long baseball game."

Opponents of the law said the ruling sends a strong message to other states hoping to replicate the law. Lawmakers or candidates in as many as 18 states say they want to push similar measures when their legislative sessions start up again in 2011.

"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 The Associated Press. "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.'"

But a lawmaker in Utah said the state will likely take up a similar laws anyway.

"The ruling ... should not be a reason for Utah to not move forward," said Utah state Rep. Carl Wimmer, a Republican from Herriman City, who said he plans to co-sponsor a bill similar to Arizona's next year and wasn't surprised it was blocked. "For too long the states have cowered in the corner because of one ruling by one federal judge."

Contributing to this report were Associated Press Writers Michelle Price, Paul Davenport and Jacques Billeaud in Phoenix, and Sara Kugler Frazier in New York.