WASHINGTON - The Supreme Court on Monday upheld part of Arizona's strict border-control law, which compels the state's law enforcement officers to check the residency status of people they suspect are in the country illegally. In a complex decision that's likely to spur similar crackdowns in other states, the court struck down some of Arizona's law while saying it was too soon to say whether the most controversial status checks went too far.

"The nature and timing of this case counsel caution in evaluating the validity" of the law, Justice Anthony Kennedy wrote for the majority, adding that "at this stage, there is a basic uncertainty about what the law means and how it will be enforced."

The law requires Arizona law enforcement personnel who've detained individuals for other legitimate reasons to check their residency status if the officers have a "reasonable suspicion" that the detainees are illegal immigrants. When someone is arrested, residency status must be confirmed before the person is released. This section now can go into effect, after which other legal challenges can be filed.

The Arizona Support Our Law Enforcement and Safe Neighborhoods Act also makes it a state crime to be in the United States without authorization, as well as a state crime for an illegal immigrant to work or seek work without authorization. The Supreme Court struck down these provisions as intrusions on federal authority.

"Arizona may have understandable frustrations with the problems caused by illegal immigration," Kennedy acknowledged, "but the state may not pursue policies that undermine federal law."

Five justices agreed, three justices disagreed in whole or in part and one justice did not participate.

"The issue here is a stark one," Justice Antonin Scalia wrote in dissent. "Are the sovereign states at the mercy of the federal executive's refusal to enforce the nation's immigration laws?"

Citing congressional failures to deal effectively with immigration, as well as the estimated 11 million illegal immigrants who live in the United States, Arizona legislators included several far-reaching provisions in the 2010 law.

The Obama administration sued to block the law even before it took effect, arguing that the state was intruding on the federal government's authority to secure borders and set immigration policy. The 9th U.S. Circuit Court of Appeals had sided with Obama and struck down the law. The circuit, covers nine Western states, is the nation's largest and in many years it's the most frequent to be reversed by the Supreme Court.

South Carolina, Idaho, Florida and 13 other states allied with Arizona, arguing for the power to impose certain immigration measures if they chose. House of Representatives Minority Leader Nancy Pelosi and 16 other House Democrats from California took the opposite tack. On both sides, dozens of amicus briefs pressed different points.

While the ruling is a partial legal defeat for Obama, some scholars predict that the court's unwillingness to strike down all of Arizona's law could help the president politically by boosting turnout in next fall's election among the nation's 21 million voting-age Hispanics.

"Fear," Gary Segura, a Stanford University pollster and political science professor, said earlier this year, "is a remarkable mobilizer."

Democratic Sen. Charles Schumer of New York already has promised to introduce a bill rebutting the court. The measure has no chance of passing this year through a divided Congress, but it could sharpen a debate that Democratic strategists such as Schumer think can help them among Hispanic voters.

In another move alluring to Hispanic voters, Obama used his presidential authority earlier this month to protect hundreds of thousands of young illegal immigrants from potential deportation. Obama's action covered immigrants younger than 30 who'd entered the United States before they were 16.

Justice Elena Kagan didn't participate in the case, the last one to be argued during the term that began last October, as her former colleagues in the solicitor general's office had tried to block Arizona's law.

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