SAN FRANCISCO — California prisoners seeking parole will have a tougher time getting help from the federal courts under a Supreme Court decision delivered today.

The court unanimously reversed two Ninth Circuit U.S. Court of Appeals decisions, saying the federal courts had no business second-guessing the state’s parole determinations. Parole, the justices said, is not a federal constitutional right, and habeas corpus relief is not available for an error of state law.