Many supporters of cameras in the courts consider the federal bench to be the last great bastion to conquer. Last September, as pretrial testimony in the Simpson case saturated the airwaves, the judges who set the rules for federal courts stunned observers by rejecting a strong recommendation that cameras be allowed in federal proceedings. The recommendation was a result of a three-year experiment with cameras that began in July 1991. Six district courts allowed cameras to record civil proceedings for the first time to determine the impact of the technology. As the experiment ended, a Federal Judicial Center study concluded that the experiment had been a great success. Ninety-eight percent of the district court judges who took part found the presence of the camera had no or only a minor effect on court decisions. Ninety percent of the judges said it had no or only a minor impact on their own decisions. But where witnesses were concerned, there was far less unanimity. Almost 30 percent of the judges raised concerns about the cameras' impact on witnesses' protection and attention spans. More than 40 percent said it had an impact on witnesses' willingness to appear. A committee of federal judges reviewed the study and recommended to the full United States Judicial Conference (the 27 judges who make the rules for the federal courts) that cameras be allowed in all federal courts beginning in May 1995 in accordance with a strict set of standards. To the surprise of many, the full conference voted 2 to 1 against allowing cameras in the courts. ''The judges felt any impact on witnesses and jurors, however small, was significant enough to outweigh any argument in favor of having cameras in the courtroom,'' says David Sellers, spokesman for the Administrative Office of the US Courts. This spring, the committee reiterated its belief that cameras should be allowed, but there has been no further action on the matter. According to Mr. Sellers, none is expected in the near future.