A federal appeals court ruled Monday that the most contested provisions of an Arizona immigration law passed last year will remain blocked from taking effect, handing the Obama administration a victory in its efforts to overturn the legislation.

The U.S. Court of Appeals for the 9th Circuit upheld a lower court ruling that put on hold key provisions of the Arizona law, which empowers police to question people whom they have a “reasonable suspicion” are illegal immigrants. The measure has triggered a fierce national debate, and the legal case is being watched by other states and advocates on both sides of the issue.

In a split decision, a three-judge panel found that U.S. District Judge Susan R. Bolton “did not abuse” her discretion in blocking parts of the law that, among other things, require police to check immigration status if they stop someone while enforcing other laws.

The court ruled only on Bolton’s order, not on whether the Arizona measure is legal, and the Justice Department’s move to have the law thrown out will proceed. But the judges gave strong indications that they accept the administration’s argument that the legislation is unconstitutional and that they would rule that way in the end.

“The Arizona statute before us has become a symbol,’’ Judge John T. Noonan wrote in a concurring opinion. “For those sympathetic to immigrants to the United States, it is a challenge and a chilling foretaste of what other states might attempt.’’

Judge Richard A. Paez, who wrote the majority opinion, used strong language as he appeared to endorse the administration’s position that Arizona’s law intrudes on federal immigration enforcement and is “preempted” by federal law.

“Arizona has attempted to hijack a discretionary role that Congress delegated to the Executive,’’ the decision said, adding that the Arizona law would “usurp” the U.S. attorney general’s role in directing any state enforcement of federal immigration laws.

Judge Carlos T. Bea dissented from parts of the ruling.

The decision, the first appellate action on the much debated law that Arizona Gov. Jan Brewer (R) signed in April 2010, makes it highly likely that the Justice Department will prevail in the 9th Circuit, which has a majority of Democratic-appointed judges, legal experts said.

“I believe this will control the outcome of the case,’’ said Louis Moffa, a professor at Rutgers School of Law and an expert on immigration and constitutional law. “The court’s language is pretty stark.’’

Extended struggle

The ruling is also one of the first steps in a legal struggle expected to play out over several years. Brewer has vowed to take the case to the U.S. Supreme Court and could appeal Monday’s decision to the full 9th Circuit.

In a joint statement, Brewer and Arizona Attorney General Tom Horne (R) said they are “considering their legal options” and that they remain confident the law will eventually be found constitutional. Monday’s ruling “does harm to the safety and well-being of Arizonans who suffer the negative effects of illegal immigration,’’ they said.

Justice Department spokesman Matthew Miller said the department is “pleased with the court’s decision.’’

The decision did not break down along strict partisan lines. Paez is a Democratic appointee, but Noonan was appointed by President Ronald Reagan, a Republican. Bea is a Republican appointee who tends to vote with the court’s conservative wing.

Objections raised

In her July ruling, Bolton blocked provisions of the Arizona law that also allow for warrantless arrests of suspected illegal immigrants and would criminalize the failure of immigrants to carry registration papers. Civil rights groups and federal lawyers had objected to those provisions in particular, while Arizona officials defended them as necessary to fight a tide of illegal immigration.

Bolton allowed other provisions to take effect, including one making it a crime to obstruct traffic to pick up day laborers.

The Justice Department lawsuit, filed in July, was a rare assertion of federal power that sets up a clash with a state on one of the nation’s most divisive political issues. The lawsuit said the Arizona measure conflicts with federal law, would disrupt immigration enforcement and would lead to police harassment of those who cannot prove their lawful status.

Arizona has defended the law’s constitutionality and accused the federal government of refusing to solve the state’s illegal immigration problem.

Lawmakers across the country had vowed to copy Arizona’s strict crackdown, but state budget deficits coupled with the federal challenge and the political backlash have made passage of such statutes uncertain.

Omar Jadwat, an attorney for the American Civil Liberties Union — which represents civil rights groups also challenging the Arizona law — said Monday’s ruling would probably affect states still considering such laws.

“It sends a very clear message that what Arizona tried to do just can’t be done in a constitutional way,’’ he said. “It would be folly not to pay attention to that.’’