THE WOULD-BE ASSASSIN

When he shot the president on March 30, 1981, did John W. Hinckley Jr. suffer from a mental illness that prevented him from either understanding his action or obeying the law?

Dr. Sally A.C. Johnson, a government psychiatrist, conceding that Hinckley had personality disorders, testified that he was in control of his behavior.

Defense psychiatrists said Hinckley suffered from severe depression, delusions and schizophrenia. Dr. William T. Carpenter Jr. said Hinckley's actions were controlled by the "inner dictates of an inner world." Other defense psychiatrists testified that Hinckley thought his act would bring about a union with actress Jodie Foster.

The jury declared him legally insane.

THE TWINKIE DEFENSE

Dan White, a former policeman and fireman and city superviser, shot and killed San Francisco mayor George Moscone and city supervisor Harvey Milk on Nov. 27, 1978. Did junk food play a role?

He was seeking reinstatement to the Board of Supervisors but knew Moscone planned to refuse.

White pleaded innocent to first-degree murder, and his lawyer said he suffered from "diminished capacity" -- aggravated by junk food. Prosecution psychiatrist Dr. Roland Levy, who interviewed White a few hours after the two killings, said: "There was nothing in my interview to suggest any sort of mental disorder."

White was convicted of manslaughter, spent five years in prison and was paroled. He committed suicide in 1985. The "Twinkie Defense" was banned. THE ABDUCTED HEIRESS

Patricia Hearst was abducted by the Symbionese Liberation Army on Feb. 4, 1974, and later participated in a bank robbery with her captors. She said she was brainwashed.

Hearst was assaulted, isolated from family and friends and locked in a closet for six weeks. Dr. William Sargant, a British psychiatrist, examined Hearst and said she suffered from the same stresses caused by wartime brainwashing. In The Times of London, he wrote: "There will never be any doubt in my own mind that Patty Hearst was . . . 'coerced in thought and deed.' "

A prosecution witness, Dr. Joel Fort, said Hearst was "a voluntary member" of the SLA.

In 1976, Hearst was convicted. In 1979, President Carter commuted her seven-year sentence.

THE SPY CASE

Whittaker Chambers, a Time magazine writer and confessed Communist spy, was the chief accuser of Alger Hiss. To clear himself, Hiss sought to discredit Chambers.

Dr. Carl Binger, testifying in defense of Hiss at his 1948 perjury trial, said Chambers had a psychopathic personality and made false accusations about people. Binger stated that the number of times Chambers looked at the ceiling was evidence of his mental illness.

The prosecution discredited the testimony by counting the number of times Binger himself looked at the ceiling.

Hiss was convicted of perjury and served 44 months in prison.