Prosecutors and criminal defense lawyers clashed in hearings at the Senate Judiciary Committee yesterday over various proposals to limit the use of the insanity defense in federal court.

"To modify the insanity defense is not to take a step backward, but rather to understand more about the limits of psychiatry," said John H. Maynard, Montana assistant attorney general, recommending that the committee adopt a bill similar to a 1979 Montana law that essentially abolished the insanity defense.

Under that law, Maynard said, juries aren't confronted with a barrage of conflicting psychiatric testimony, and "if a person is aware of the fact that he is shooting someone, he is guilty of that crime."

Attorney General William French Smith endorsed that basic approach at a hearing before the committee last week, saying it would eliminate the insanity defense as far as the Constitution allows.

But William J. Mertens of the National Legal Aid and Defender Association argued yesterday that holding a criminal defendant responsible could prove senseless and unjust if, for example, he so lacked "a meaningful comprehension of what he is doing that it is unjust to punish him."

"Is it sensible to make guilt hinge in this way on the specific content of a person's insane delusions?" Mertens, chief of the appellate division of the D.C. Public Defender Service, asked. "I do not think so."

While defense lawyers argued that the committee should retain the insanity defense in its current form, much of the debate yesterday, as at the committee's earlier hearings, did not involve whether the committee should cut back on the insanity defense but what form the new limitations ought to take.

Among the other proposals, fueled last month by the acquittal of attempted presidential assassin John W. Hinckley Jr., are shifting the burden of proof in insanity cases from the prosecution to the defense, and adopting new verdicts of "guilty but insane," or "guilty but mentally ill," which would allow convicted criminals to receive psychiatric help but still make certain they are punished.

Austin, Tex., criminal lawyer Frank Maloney, representing the National Association of Criminal Defense lawyers, said the judge's instructions to the Hinckley jury were tilted in favor of the prosecution and could have resulted in a reversal on appeal had Hinckley been convicted.

Indiana Attorney General Linley Pearson, representing the National Association of Attorneys General, and William L. Cahalan, prosecuting attorney for Wayne County, Mich., told the committee it should shift the burden of proof and adopt a verdict of "guilty but mentally ill," as Indiana and Michigan have done.

Under a "guilty but mentally ill" verdict, criminal defendents so deranged they had no idea of what they were doing could still be acquitted, but those with a lesser degree of mental illness would be convicted and then sent either to mental institutions or prisons, depending on testing after trial. Hospitalized defendants who later recovered from the mental illness would be sent to jail to serve the remainder of their terms.

"I am convinced that if the verdict had been available to the jurors in the Hinckley case, they would have found him 'guilty but mentally ill,' " and Hinckley could have been held "criminally responsible" for his actions, Cahalan said.