Somewhere in America are people who are pleased that John W. Hinckley Jr. has been found not guilty. His family, of course, and his defense lawyers and the psychiatrists who testified on his behalf. Also perhaps Edward Thomas Mann. Mann is accused of killing three and wounding six in a shooting spree at the Bethesda IBM building where he used to work. His lawyer has indicated Mann, like Hinckley, will plead not guilty by reason of insanity. If Hinckley had been convicted, Mann wouldn't have had a prayer. Now, who knows?

But leaving aside those with a personal interest in the two cases, it's hard to find anyone who believes the not guilty verdict makes sense. True, anyone who plots to kill a famous person against whom he has no grudge, in the hope that the act will make him famous and thereby impress a young actress he has never met, is, at least by my lights, certifiably insane. So is a man who lives a quiet, apparently normal life, and then suddenly drives his automobile through the glass doors of an office building and, during a 71/2-hour siege, fires 150 shots at people he doesn't know.

Hinckley supposedly was crazy as a result of his unrequited love for actress Jodie Foster. Mann, one supposes, will claim he was driven out of his mind by the racism of his former employer. But should Hinckley, who admitted firing on the presidential party, have been acquitted because of his insanity? Should Mann, assuming he in fact did what he is accused of having done, be found not guilty by reason of insanity?

My own verdict might be along the lines of an option recently enacted in Georgia: guilty but insane-- leaving it to the judge to decide how much of the sentence should be served in a mental hospital and how much in the slammer. I wouldn't want to be too hard on the jury that returned the verdict in the Hinckley case. After all, the jurors' instructions were that if the prosecution hadn't established to their certainty that the defendant was sane, they should return a not guilty verdict. Even so, it took them some 24 hours over a four-day period to reach a conclusion. And no wonder. Who can be certain beyond reasonable doubt that anybody who kills, or maims, or rapes, or commits any of a number of particularly heinous crimes is sane? But surely it does not follow that such offenses should go unpunished.

Not that I would rule out insanity defenses altogether. I would vote to acquit a 2-year-old child (or an adult with the mental capacity of a 2-year-old) who pointed a gun at you and pulled the trigger. I'd assume he didn't understand the consequences of his act. I would have voted to acquit Hinckley if his lawyers had convinced me that he thought he was spraying water, rather than bullets, on the Reagan party. But if I am persuaded that the defendant knew what he was doing and intended to do it, I am persuaded of his guilt.

Having said that, I must add that most of the fears expressed over insanity pleas are overblown. To begin with, the insanity defense is rarely used successfully, although a few cases draw a good deal of attention. Even where insanity is successfully invoked, defendants aren't that much better off. A recent review by the National Law Journal discloses that those found not guilty by reason of insanity usually spend more time in a mental hospital than they would have spent in jail on a verdict of guilty.

Probably the greatest harm done by a successful insanity plea is to the public perception of justice. Anyone who follows the psychiatric gibberish of the experts testifying for and against the defendant can be forgiven for concluding that the system itself is crazy.