WASHINGTON — The Supreme Court tpday 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 5-3 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.”