SAN FRANCISCO  Gov. Jan Brewer of Arizona and her team of lawyers defended the state’s strict new immigration law in a federal appeals court on Monday, facing a panel of three judges who sharply questioned the way the law would be carried out. Lawyers from the Justice Department argued that central parts of the state law were unconstitutional and would interfere with federal law enforcement.

In July, just one day before the law was to take effect, a lower court suspended parts of it, ruling that the state could not require local law enforcement officials to check on the immigration status of people they stop and detain them if they were suspected of entering the country illegally.

Ms. Brewer is appealing that decision. Whatever the outcome from the United States Court of Appeals for the Ninth Circuit here, it, too, is expected to be appealed, and Ms. Brewer has said she will take it to the Supreme Court if necessary.

During Monday’s hearing, the appellate judges abruptly ended a discussion of a provision of the state law that would forbid illegal immigrants to work in the state, saying that a decision in another case had already blocked the state from making it a crime for such immigrants to seek employment.