THE HINCKLEY verdict has prompted a reasessment of the insanity defense, not only by judges and legislators, but also by the two professions most concerned with this aspect of the criminal justice system. Last month, the American Psychiatric Association issued a report urging revisions in the legal definition of insanity and emphasizing that psychiatrists are medical experts, not legal ones. They are qualified, said the doctors, to present medical information and to give opinion about the mental state of an accused person. But they cannot predict future behavior or assign legal guilt.

Now, two committees of the American Bar Association--the Standing Committee on Standards for Criminal Justice and the Commission on the Mentally Disabled--have recommended changes in that association's traditional position of support for the insanity standard used in the Hinckley trial. These proposals will be presented to the ABA House of Delegates at its midyear meeting later this month. Because the current standard still has many supporters, the proposed revisions are controversial, and the debate will be hot.

The committees' recommendations focus on three factors: a new definition of criminal insanity, strong opposition to the elimination of the defense in cases where the accused could not appreciate the nature of his act, and a discussion of the burden of proof. It is the first proposal that is of particular interest, though, since it reflects many of the same concerns expressed by the psychiatrists.

The Hinckley jury was told to acquit the defendant if "he lacks substantial capacity either to appreciate the criminality of his conduct or to conform his conduct to the requirements of the law." It is the latter clause--the one that requires a judgment as to the defendant's will rather than his knowledge-- that is now questioned by both the doctors and the lawyers.

"Most academic commentary upon this subject during the past decade continues to question the scientific basis for assessments of volitional incapacity," argue the lawyers, and "it is just this volitional or behavioral part of the ALI (American Law Institute) test that has brought the insanity defense under increasing attack. . . . Yet, experience confirms that there is no accurate scientific basis for measuring one's capacity for self-control. . . . There is, in short, no objective basis for distinguishing between offenders who were undeterrable and those who were merely undeterred." The psychiatrists had put it another way: "The line between an irresistible impulse and an impulse not resisted is probably no sharper than that between twilight and dusk." The judgment of the ABA committees is clear: "In our opinion, to even ask the volitional question invites fabricated expert claims, undermines the equal administration of the penal law and compromises the law's deterrent effect."

Criminal defense attorneys, who are well represented in the ABA House of Delegates, are sure to oppose these revisions. But surely the ABA delegates will have in mind not only the recommendations of two of their own committees but the unanimous report of the American Psychiatric Association board as well. In this case, the doctors have offered expert testimony that should be given great weight.