The Supreme Court on Monday struck down several provisions of Arizona's immigration law but upheld its most controversial element, a requirement that local police check the immigration status of anyone they suspect is in the country illegally.

In reviewing a law that served as a model for immigration statutes in several other states, the court struck down a provision that required immigrants to carry documents proving legal residency. It also struck a provision that made it a crime for an illegal immigrant to pursue or hold a job in Arizona and another that allowed local law enforcement to arrest illegal immigrants without a warrant.

But the court upheld the so-called "show me your papers" requirement that allows police to check the status of anyone they stop if there is "reasonable suspicion" that the person is in the country illegally.

President Obama, whose administration challenged the Arizona law, said he was pleased the court threw out three of the four provisions it considered, but remained "concerned about the practical impact of the remaining provision."

Senate Majority Leader Harry Reid, D-Nev., said the surviving provision could lead to racial profiling by Arizona law enforcement.

"With three out of the four provisions being struck down, the ruling shows that the Obama administration was right to challenge this law, which was not just ill-advised but also unconstitutional," Reid said.

Backers of Arizona's law, however, celebrated the court's unanimous decision to uphold what many consider to be the centerpiece of the law.

Arizona Gov. Jan Brewer, a Republican who has literally gone toe to toe with Obama in demanding more federal enforcement of immigration laws, on Monday called the provision "the heart" of the law and praised the court for upholding it.

"Today is a day when the key components of our efforts to protect the citizens of Arizona, to take up the fight against illegal immigration in a balanced and constitutional way, has unanimously been vindicated by the highest court in the land," Brewer said.

While the split decision allowed both sides of the immigration debate to claim victory, experts questioned how much either side won.

"As with immigration policy generally, it's really hard to say who the winners and losers are," said Ilya Shapiro, a senior fellow in constitutional studies at the Cato Institute, a libertarian think thank. "What the court is saying is that any real substantial immigration reform has to come from lawmaking, not from executive policymaking."

Arizona is one of the states hardest hit by illegal immigration and the crime resulting from it, a fact acknowledged by Justice Anthony Kennedy in the majority opinion.

But several other states have since adopted similar laws, including South Carolina, Utah and Alabama, and Monday's ruling is certain to shape their enforcement procedures. South Carolina Attorney General Alan Wilson called the ruling "a major victory."

The ruling came just after Obama announced his administration would no longer deport illegal immigrants who were bought to this country by their parents, a policy Justice Antonin Scalia sharply criticized in a 22-page dissenting opinion.

"To say, as the Court does, that Arizona contradicts federal law by enforcing applications of the Immigration Act that the president declines to enforce boggles the mind," Scalia said.