"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."

More demonstrators opposed to the law planned to gather on Thursday, with the Los Angeles-based National Day Laborer Organizing Network and the immigrant-rights group Puente saying they would march from the state Capitol at dawn.

Demonstrations also are planned for outside Maricopa County Sheriff Joe Arpaio's office, said activist Salvador Reza.

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. Some lawmakers pushing the legislation said they would not be daunted by the ruling and plan to push ahead in response to what they believe is a scourge that needs to be tackled.

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 the influx of illegal migrants drains vast sums of money from hospitals, education and other services.

"We're going to have to look and see," said Idaho state Sen. Monty Pearce, a second cousin of Russell Pearce and a supporter of immigration reform in his state. "Nobody had dreamed up, two years ago, the Arizona law, and so everybody is looking for that crack where we can get something done, where we can turn the clock back a little bit and get our country back."

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."

In the meantime, other states like Utah will likely take up similar laws, possibly redesigned to get around Bolton's objections.

"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."

The core of the government's case is that federal immigration law trumps state law - an issue known as "pre-emption" in legal circles and one that dates to the founding of America. In her ruling, Bolton pointed out five portions of the law where she believed the federal government would likely succeed on its claims.

The Justice Department argued in court that the law was unconstitutional and that allowing states to push their own measures would lead to a patchwork of immigration laws across the nation and disrupt a carefully balanced approach crafted by Congress.

Arizona argues that the federal government has failed to secure the border, and that it has a right to take matters into its own hands.

For now, the federal government has the upper-hand in the dispute, by virtue of the strength of its arguments and the precedent on the pre-emption issue. The Bush administration successfully used the pre-emption argument to win consumer product cases, and judges in other jurisdictions have looked favorably on the argument in immigration disputes.

"This is clearly a significant victory for the Justice Department and a defeat for the sponsors of this law," said Peter Spiro, a constitutional law professor at Temple University who has studied immigration law extensively. "They will not win on this round of appeals. They'll get a shot after a trial and a final ruling by Judge Bolton."