WASHINGTON A strict border-control law partially drafted in Kansas and adopted in Arizona found both vindication and defeat Monday with a U.S. Supreme Court decision that upheld its most contentious provision but blocked others.

The court ultimately ruled that Arizona's state law enforcement officers can be compelled to check the residency status of people they suspect are in the country illegally.

In a complex decision that keeps immigration on the political front burner, the court struck some border-control provisions but said it was too soon to say whether Arizona went too far with the ID check requirement, dubbed "show me your papers" by the law's opponents.

"The federal government has brought suit against a sovereign state to challenge the provision even before the law has taken effect," Justice Anthony Kennedy wrote for the majority, adding that "there is a basic uncertainty about what the law means and how it will be enforced."

Legally, the 5-3 decision is a mixed bag for the Obama administration. It lost on the highest-profile challenge while prevailing on several others. Politically, that partial loss could actually help the administration by more clearly distinguishing the positions of President Barack Obama and presumptive Republican presidential nominee Mitt Romney.

The decision comes on the heels of Obama's June 15 directive to immigration officials to stop deporting certain young undocumented workers, which energized the campaign in the Hispanic community. Romney, who was a hard-liner on illegal immigration during the primary campaign, soft-pedaled his complaints about Obama's policy change.

On Monday, too, Romney steered clear of his more strident primary rhetoric. He declared during an Arizona debate in February that "the right course for America is to drop these lawsuits against Arizona and other states that are trying to do the job Barack Obama isn't doing." On Monday, he stressed that the ruling "underscores the need for a president who will lead on this critical issue and work in a bipartisan fashion."

Obama vowed to keep watch on Arizona.

"Going forward, we must ensure that Arizona law enforcement officials do not enforce this law in a manner that undermines the civil rights of Americans," he said in a statement.

The Department of Homeland Security elaborated Monday with a field directive ordering its officers to retain their current enforcement priorities, which focus on criminal aliens. Practically speaking, that means an illegal immigrant caught up by a routine Arizona ID check probably won't be put into federal detention unless he or she has another, serious criminal problem.

Citing congressional failures to deal effectively with immigration, as well as the estimated 11 million illegal immigrants who live in the United States, state legislators included several far-reaching provisions in the 2010 law called the Arizona Support Our Law Enforcement and Safe Neighborhoods Act.

Monday's ruling was a partial rebuke for state officials who had argued that they were entitled to supplement federal efforts to address illegal immigration.

One of the authors of the Arizona law is Kansas Secretary of State Kris Kobach, who has made efforts to crack down on illegal immigration a prominent part of his political identity.

"This is really the vindication of 11 years of work," Kobach said in an interview after the decision was released Monday. "Would I prefer Antonin Scalia's dissent (arguing for upholding the entire law) be the majority opinion? Sure, but this is still a very good opinion for the state (of Arizona.)"

The law requires Arizona law enforcement personnel who have stopped people 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.

In addition to the residency checks, the Arizona law made 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 law also allowed warrantless arrests of illegal immigrants who local law enforcement officers believe have committed an offense that makes them deportable from the United States.

The court struck down those 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 -- Kennedy, Chief Justice John Roberts, Ruth Bader Ginsburg, Stephen Breyer and Sonia Sotomayor -- agreed. Three justices -- Scalia, Clarence Thomas and Samuel Alito -- disagreed in whole or in part. Justice Elena Kagan didn't participate in the case, the last one to be argued during the term that began in October. Her former colleagues in the solicitor general's office had tried to block Arizona's law.

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

In Kansas and Missouri, the reaction was predictably mixed depending on views about immigration policy.

"It's good that the Supreme Court upheld that the state could pass laws that would allow the law enforcement officer to check citizenship, even when they just pull someone over," said Missouri state Sen. Will Kraus, a Lee's Summit Republican who has proposed immigration reforms. "We know immigration is a federal issue. What I hope is that the federal government takes it more seriously and actually enforces the law."

Kansas state Rep. Charlotte O'Hara of Overland Park, also a Republican, said she didn't like what she saw as the ruling's diminishment of states' rights.

"When you go back to our founding fathers, the intent was the states are the sovereigns," she said. "When you talk about illegal immigration and the impact on our states in terms of the budget ... it's very detrimental to the state of Kansas."

Those on the opposite side of the issue were set back by the way the court upheld the central provision set down in Arizona law -- and likely to be imitated in other states.

"Somebody can stop me and say I think you're a suspicious character, and pull your papers. Show me your documentation," said Cris Medina of Guadalupe Center in Kansas City. "That is very unfair. That's stereotyping people. Instead of this country making progress, we're taking two steps backward."