A divided Supreme Court set guidelines Friday for when judges should disqualify themselves from cases, calling on judges everywhere to help "maintain public confidence in the impartiality of the judiciary."

The 5-4 ruling by Justice John Paul Stevens involved a federal judge in Louisiana who ruled in a hospital ownership case affecting Loyola University while he was a member of the school's board of trustees.The 5th U.S. Circuit Court of Appeals eventually vacated the ruling by Judge Robert Collins after concluding his participation in the case presented a possible conflict of interest.

In affirming the lower court, Justice John Paul Stevens said a judge's ruling should be reversed whenever "a reasonable person" knowing the relevant facts would have doubts about the judge's impartiality - even if the judge was not actually aware of any conflict.

If a judge becomes aware of a conflict after a ruling is handed down, he or she should vacate the decision, Stevens said.

"This reading of the statute does not call upon judges to perform the impossible - to disqualify themselves based on facts they do not know," Stevens said. "Rather, ( judge) is called upon to rectify an oversight and to take the steps necessary to maintain public confidence in the impartiality of the judiciary."

The case forced the court to interpret provisions in the Judicial Code passed by Congress in 1974, which states that a judge should disqualify himself "in any proceeding in which his impartiality might reasonably be questioned."

Four justices dissented from the ruling. They were Chief Justice William Rehnquist and Justices Byron White, Antonin Scalia and Sandra Day O'Connor.