PHOENIX — The United States could see an official about-face in the coming months in how it confronts illegal immigration if the Supreme Court follows through on its suggestion that it would let local police enforce the most controversial part of Arizona’s immigration law.

Over the last several years, states frustrated with America’s porous borders have rejected the long held notion that Washington is responsible for confronting illegal immigration and have passed a flurry of laws to let local police confront illegal immigration. The Supreme Court is poised in the coming months to let the states know whether they haven’t crossed the line.

The justices strongly suggested Wednesday that they are ready to let Arizona enforce the most controversial part of its law, a requirement that police officers check the immigration status of people they suspect are in the country illegally. Such a ruling could codify the type of local enforcement that some local authorities in Arizona have carried out over the last six years and open the door to such enforcement in states with similar laws, such as Alabama, Georgia, Indiana, South Carolina and Utah.

“I think you’ll see more involvement by local police in immigration enforcement, an involvement that hadn’t previously been seen,” Kevin Johnson, law school dean at the University of California-Davis and an expert in immigration law, said of the possibility of Arizona’s law being upheld.

The most controversial parts of the Arizona law were put on hold by a federal judge shortly before they were to take effect in late July 2010, but the statute has encouraged other states to take up similar legislation and — combined with other state immigration laws and an ailing economy — played a part in 170,000 illegal immigrants leaving Arizona since 2007.

“If you want to turn around this invasion, then (you should) do attrition through enforcement,” said former state Sen. Russell Pearce, architect of the 2010 law and the driving force behind other Arizona immigration laws, echoing the stated purpose of the 2010 state law.

Arizona has argued it pays a disproportionate price for illegal immigration because of its 370-mile border with Mexico and its role as the busiest illegal entry point into the country.

The Obama administration, which challenged the law, said the law conflicts with a more nuanced federal immigration policy that seeks to balance national security, law enforcement, foreign policy, human rights and the rights of law-abiding citizens and immigrants. Civil rights groups that back the administration say Arizona’s and the other states’ measures encourage racial profiling and ethnic stereotyping.

A decision in the case is expected in late June.

Arizona Attorney General Tom Horne, whose office has helped defend the law, predicted the Supreme Court will uphold the law because many of its provisions mirror existing federal laws and that a year from now the state will see even less illegal immigration. “You won’t see anything that noticeable as far as law enforcement goes,” Horne said. “But you will see less people sneaking across the border.”

The Supreme Court’s comments on the most controversial requirement in Arizona’s law surprised state officials who had supported the law and had thus far lost all major court battles over the law. “I think we’ll win. It’s just how big we win,” Pearce said.

Immigrant rights advocates, who believed the courts would reject attempts by states to grab more law enforcement power, also were surprised and said a validation of the law by the Supreme Court would frighten immigrants further and cause Latinos who are here legally to be asked about their immigration status.

“The crisis here in Arizona would only multiply,” said Carlos Garcia, organizer of an immigration march that drew several hundred people in downtown Phoenix on Wednesday. Authorities said at least nine people were arrested for blocking a street and refusing to move. “It would mean that anyone, as they are leaving their home — whether they are going to work, to church, wherever they are going — could be asked for their documents.”

During arguments Wednesday over the Arizona law, liberal and conservative justices reacted skeptically to the Obama administration’s argument that the state exceeded its authority when it made the records check, and another provision allowing suspected illegal immigrants to be arrested without a warrant, part of the Arizona law aimed at driving illegal immigrants elsewhere.

It was unclear what the court would do with other aspects of the law that have been put on hold by lower federal courts. The other blocked provisions make it a state crime for immigrants not to have immigration registration papers and for illegal immigrants to seek work or hold a job.

Peter Spiro, a Tempe University law professor who specializes in immigration law, predicted the court would uphold the police check of immigration status in Arizona’s law, but said he wouldn’t be surprised if the court threw out a provision making it a crime to be without immigration documents.

Such a ruling would let police question people about their immigration status if they have good reason to do so, but police would have to call federal authorities to see if they would want to pick up anyone found to be in the country illegally. If federal agents decline, officers would have to release the people, unless they were suspected of committing crimes, Spiro said.

If that happened, the law would be mostly symbolic, but would still carry some significance for immigrants, Spiro said.

“It would make it clear that Arizona is unfriendly to undocumented aliens,” Spiro said.