A federal appeals court is handing a major legal victory to the New York Times by rejecting a former Army scientist’s claim that he was libeled by the newspaper in columns linking him to anthrax-laden mailings that killed five Americans in 2001.

The 4th U.S. Circuit Court of Appeals, based in Richmond, Va., agreed with a lower court that the scientist, Dr. Steven Hatfill, was a public figure in the national debate over bioterrorism preparedness. As a public figure, Dr. Hatfill could only win his suit by proving that the Times deliberately lied about him or knew that it was likely the information it was printing was false. Dr. Hatfill could not meet that burden and was not entitled to a trial, the three-judge appeals court panel said in its unanimous ruling yesterday.

“Throughout his career, Dr. Hatfill was not only repeatedly sought out as an expert on bioterrorism, but was also a vocal critic of the government’s unpreparedness for a bioterrorist attack, as evidenced by the topics of his lectures, writings, participation on panels, and interviews,” Judge Paul Niemeyer wrote, joined by judges M. Blane Michael and Clarence Beam. “Through these media, Dr. Hatfill voluntarily thrust himself into the debate. He cannot remove himself now to assume a favorable litigation posture.”

Judge Niemeyer said the author of the columns, Nicholas Kristof, wasn’t libeling Dr. Hatfill because the columnist had strong reason to consider the scientist to be the lead suspect. “Indeed the record contains substantial evidence to support The New York Times’ contention that Kristof actually believed that Dr. Hatfill was the prime suspect,” the judge wrote.

Dr. Hatfill’s lawyers argued that even if he had voluntarily taken a public role in the bioterrorism debate, that did not render him a public figure for articles about the investigation into the anthrax attacks. The court disagreed, finding that Mr. Kristof’s columns, some of which referred to the scientist as Mr. Z, discussed the investigation in a broader national security context.

The lawsuit was a tightrope walk for the Times, particularly because Mr. Kristof refused to identify his confidential sources for the columns. The district court judge who handled the case, Claude Hilton, imposed a fairly mild sanction on the Times and simply barred the newspaper from relying on information from the unidentified sources.

Dr. Hatfill’s lawyers said the Times’s defiance should have been punished more sternly, but the appeals court panel said yesterday that the district court’s action “did not amount to an abuse of discretion.”

“This leaves Hatfill with no remedy for an accusation that virtually everyone now understands to have been a horrible miscarriage of justice,” a lawyer for Dr. Hatfill, Thomas Connolly, wrote in an e-mail to The New York Sun yesterday. “If Steven Hatfill was a public figure when Kristof wrote about him, then so are we all.” The lawyer said Dr. Hatfill would pursue the case further, presumably to the appeals court’s full bench or to the Supreme Court.

The Times hailed the ruling as logical result of a 1964 Supreme Court decision which established the “actual malice” standard for libel cases involving public figures. “We think it’s an important reaffirmation of Times v. Sullivan, which is intended to enourage vigorous discussion of public events,” a lawyer for the paper, David McCraw, told the Associated Press.

The FBI carried out several searches for evidence linking Dr. Hatfill to the anthrax-laden mailings. However, neither he nor anyone else was ever charged in the case.

Last month, the federal government agreed to pay $5.8 million in cash and future annuity payments to resolve a Privacy Act lawsuit in which Dr. Hatfill accused government officials of illegally releasing information about him to the press. The stories came from anonymous leaks and an unusual public statement in which the attorney general at the time of the attacks, John Ashcroft, openly described Dr. Hatfill as a “person of interest” in the investigation. Even as it settled the protracted litigation, the government denied violating Dr. Hatfill’s rights.

Dr. Hatfill’s suit against the government drew significant attention because a former reporter for USA Today, Toni Locy, faced potentially ruinous fines for refusing to name her sources for articles about the investigation. The contempt ruling against Ms. Locy was on appeal when the case was settled.