Washington ? The National Academy of Sciences is warning that the FBI’s treatment of a respected Texas scientist could intimidate other researchers, hindering the study of diseases, such as plague, that are spread by toxins.

The academy’s human rights committee protested to Atty. Gen. John Ashcroft about the Justice Department’s investigation and prosecution of Thomas Butler, one of the nation’s top plague researchers.

Butler is free on $100,000 bond while awaiting trail on 15 charges, including smuggling, lying to investigators and illegal transport of hazardous biological material — in this case, live plague bacteria.

He is on paid administrative leave from his job as chief of the infectious diseases division at Texas Tech University and is prohibited from visiting his laboratory.

A federal indictment, issued in April, alleges that Butler smuggled 30 vials of plague bacteria from Tanzania and illegally transported them within the United States and abroad. The indictment also charges that he lied to FBI agents about the samples’ disappearance.

The New York Times reported Saturday that the Committee on Human Rights, which also has members from the National Academy of Engineering and the Institute of Medicine, was asking academy members to express their support for Butler in letters to Ashcroft and Robert Mueller, the FBI director.

Since Butler’s indictment, many of his colleagues have contended the charges prove that he is absent-minded but not criminal.