AT A RECENT meeting of state chief justices, Associate U.S. Attorney General Rudolph Giuliani told his audience that the jury verdict in the Hinckley case was a benefit to American society since it had provoked a public debate on the insanity defense. Mr. Giuliani may be more sanguine than most about that particular verdict but he is right that the public's and lawyers' attitudes toward the defense have changed a lot since that acquittal.

First the American Psychiatric Association, representing people most subjected to criticism after the Hinckley trial, issued a thoughtful and practical report urging revisions in the defense. A few weeks later, two committees of the American Bar Association recommended similar changes, and, despite the opposition of some members of the defense bar, the new position was adopted by the ABA House of Delegates at its just-completed meeting in New Orleans. The Justice Department has set aside an earlier position recommending the abolition of the insanity defense and joined the organized psychiatrists and lawyers in supporting modifications. This is a formidable coalition that should exert great influence on Congress and state legislatures.

Here is the change that these medical and legal people who specialize in this area want to make: the rule in federal courts and in most states now allows acquittal of a defendant found "to lack 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, relating to a person's ability to resist committing an unlawful act, that is now called into question. More of those involved with the issue tend to concede that it is not possible scientifically to make any such judgment and think that allowing acquittal on the basis of this claim invites fraudulent testimony and confuses the public. Acquittal should be available only in cases where the accused did not know that he was committing a criminal act.

The American legal system has just about come full circle on the insanity defense in the last 30 years. With increasing knowledge of mental disorders and growing hope and compassion for those who suffer from such illness, the law had become more lenient and perhaps too reluctant to assess blame when defendants suffered from mental or personality disorders. Even before the Hinckley case, some states had adopted tougher standards and a few had abolished the insanity defense altogether. Abolition swings the pendulum too far, but the kind of change now supported by psychiatrists, lawyers and the administration may very well be just the blessing Mr. Giuliani envisions.