By a 5 to 4 vote, the Supreme Court ruled yesterday that federal employees have a right to union representation when questioned by an agency inspector general.

The justices said that a federal statute requiring union representation when a worker is interrogated by agency officials extends to situations where the investigator is an agent from the agency's Office of Inspector General, despite the traditionally independent IG role.

"The interest in fair treatment for employees under investigation is equally strong whether they are being questioned by employees in [the] OIG or by other representatives of the agency," Justice John Paul Stevens wrote in the case arising from an IG probe at the National Aeronautics and Space Administration.

The court compared the inspector general to agency management, saying the IGs act for the benefit of the agency. Established by law in 1978 to curb waste and management abuses in the bureaucracy, the IGs have traditionally considered themselves independent players in their agencies, in part because they cannot be easily fired and because they report not only to agency heads but directly to Congress.

Yesterday's case began in 1993, when NASA's IG was pursuing a report that an employee of the George C. Marshall Space Flight Center in Huntsville, Ala., sent documents threatening harm to co-workers. When the employee was interviewed, the investigator said a union official could be present but forbade him to offer the employee any advice.

The American Federation of Government Employees (AFGE) filed an unfair labor practice charge against NASA and the IG. The Federal Service Labor-Management Relations Statute gives workers the right to union representation at "any examination . . . by a representative of the agency . . . if the employee reasonably believes that the examination may result in disciplinary action."

The Federal Labor Relations Authority sided with the union against NASA, saying union officials' actions could not be restricted, and the U.S. Court of Appeals for the 11th Circuit affirmed the finding. Yesterday's high court decision upholds that position.

Joining Stevens were Justices Anthony M. Kennedy, David H. Souter, Ruth Bader Ginsburg and Stephen G. Breyer. Dissenting were Chief Justice William H. Rehnquist and Justices Clarence Thomas, Sandra Day O'Connor and Antonin Scalia.

Thomas, who is a former chairman of the Equal Employment Opportunity Commission and familiar with IG practice, wrote the dissenting statement. He asserted that an IG is supposed to be independent, serving "more than just agency concerns," and should not be considered a representative of the agency.

Reacting to the ruling in NASA v. Federal Labor Relations Authority, Stuart A. Kirsch, assistant general counsel at AFGE, said employees usually think of IGs as part of their agency's management.

"In most instances, employees are told . . .to report to the IG, then the IG tells them they are subject to discipline if they don't cooperate," he said.

Kirsch said that until the mid-1990s, when a D.C. Circuit appeals court ruling allowed IGs to deny union participation, most IGs had allowed union representatives to attend sessions where employees were questioned.

Gaston L. Gianni Jr., the IG at the Federal Deposit Insurance Corp. and vice chairman of an interagency IG group, had no immediate comment on the ruling.

Greg O'Duden, general counsel at the National Treasury Employees Union, said the decision carried special significance at the Internal Revenue Service. IRS workers were allowed to have a union representative sit in on interviews by internal investigators until last year, when Congress passed a restructuring law that created an IG for the IRS.

CAPTION: Justice Thomas wrote dissenting opinion.

CAPTION: Justice Stevens wrote of interest in "fair treatment."