PHOENIX: A federal judge Wednesday blocked the most controversial parts of Arizona`s new immigration law which would have given police the power to check the immigration status of anyone stopped on suspicion of any crime.

The ruling came hours before the law had been due to go into effect, handing temporary victory to the Obama administration which has challenged the legislation, and rights groups that said it would lead to ethnic profiling.

Judge Susan Bolton said parts of the law requiring police to check the immigration status of suspects "would likely burden legal resident aliens."

And she found there was also a "substantial likelihood that officers will wrongfully arrest legal resident aliens" due to complex deportation laws which are enforced by federal courts.

Opponents say the law is xenophobic and will lead to people being stopped on the streets simply because of the way they look.

But officials in Arizona, which borders Mexico, have argued the US administration has failed to secure the frontiers, and they are overrun by illegal immigrants.

They maintain that a lucrative people-smuggling trade across the border from Latin American countries has triggered a spiraling crime rate fed by simultaneous trafficking in drugs and guns.

Governor Jan Brewer, who signed the legislation into law in April, vowed to lodge a swift appeal, saying she would battle as far as the US Supreme Court.

"This fight is far from over. In fact, it is just the beginning, and at the end of what is certain to be a long legal struggle, Arizona will prevail in its right to protect our citizens," Brewer said in a statement.

But civil rights groups welcomed the ruling.

"It is very much a major step that will help protect the residents of Arizona against additional profiling and discrimination," said Alessandra Soler Meetze, director of the Arizona American Civil Liberties Union.

And foes of the law said plans for rallies, marches and acts of civil disobedience would proceed Thursday despite the court order blocking implementation of much of it.

The "day of action" kicks off at midnight (0700 GMT Thursday), with thousands of demonstrators from local and outside groups expected to take part in acts of civil disobedience.

Judge Bolton is currently hearing seven suits against the legislation, which for the first time in the United States -- a nation built on generations of immigrants -- would make illegal immigration a crime.

White House lawyers have argued immigration policy is exclusively the government`s responsibility and that state laws cannot trump federal rules or the US Constitution.

President Barack Obama took a strong stand against the law calling it "misguided" and ordered the Department of Justice to examine its legality.

Bolton said the US administration "is likely to succeed" in its argument and issued a preliminary injunction suspending the section of the Arizona law requiring police officers to check the immigrant status of any person they have stopped for a violation.

She also blocked a provision making it a crime to fail to apply for or carry proper papers, and a third section making it a crime for illegal immigrants to apply for or perform any work.

Bolton ruled that she was issuing the injunction because otherwise "the United States is likely to suffer irreparable harm."

If Arizona were to press ahead with the controversial sections of the law it would "interfere with federal policy," she wrote, adding it would also divert federal resources away from the government`s priorities.

Lydia Guzman, an activist with Somos America, an immigrant rights group, said she felt validated by the ruling.

"We’re going to continue do it, to work hard, until we get immigration reform," she said.

The Department of Homeland Security also welcomed the ruling saying it "affirms the federal government`s responsibilities in enforcing our nation`s immigration laws."

The row over the Arizona law has thrust the issue of the nation`s estimated 11 million illegal immigrants once more into the spotlight, amid a trail of failed attempts to bring them out of the shadows.

Recent opinion polls have found more than 60 percent of the US population support the Arizona immigration law.

One in three of the 6.6 million people in Arizona is foreign born and an estimated 460,000 are illegal immigrants, most of whom are Mexican.

Across the border in Nogales, Mexico, meanwhile Mexico was bracing for potential mass deportations as the new Arizona immigration law was due to take effect.

Local Roman Catholic leaders, Mexico and several other Latin American countries have also strenuously objected to the law.

BDST: 0920 HRS, July 29, 2010