MISSOULA (AP) — Attorneys for W.R. Grace & Co. and some of its former executives want a federal judge to keep prosecutors from calling certain experts and witnesses at their upcoming trial, arguing in part that the experts cannot specify the cause of any asbestos-related illnesses.

The attorneys, in a motion filed this week, are requesting a hearing on the matter in U.S. District Court in Missoula.

A grand jury last year charged that Grace and several of its one-time managers conspired to conceal health risks posed by asbestos at the firm’s vermiculite mine near Libby, in northwest Montana. The mine closed in 1990.

Defense attorneys want to keep prosecutors from calling 48 ‘‘victim witnesses,’’ on whom medical records have been provided, or presenting expert testimony on the witnesses’ diagnoses, according to the motion.

‘‘The government’s witness submissions and expert disclosures make clear that many of these individuals have prior occupational exposures (either at the Libby mine or elsewhere), environmental exposures in Libby before 1976 and/or indoor air exposures’’ — collectively considered ‘‘non-indictment exposures,’’ according to the motion.

A spokesman for the U.S. attorney’s office in Billings said Friday there would be no comment beyond what gets filed with the court.

The trial has been scheduled to begin this fall, though defense attorneys have sought to push it back and also requested separate trials for the defendants.