John W. Hinckley Jr. was committed to a mental institution yesterday, and his lawyers and parents said they will make no effort to seek his release until they are satisfied that he is no longer a danger to himself or society.

Their statements came as stunned and angry lawmakers demanded that Congress either change or abolish the law that allowed a jury to find the would-be presidential assassin not guilty by reason of insanity. Senate Republican leaders called for quick action to make it harder for defendants in the federal courts to raise the insanity defense.

"I think the question of the insanity plea has sort of plagued the American jurisprudence system for a long, long time," said Senate Majority Leader Howard H. Baker Jr. (R-Tenn.).

Baker and other legislators focused their criticism yesterday on the federal law that puts the burden on the prosecution--as it did in the Hinckley case--to prove beyond a reasonable doubt that a defendant was sane. Sen. Strom Thurmond (R-S.C.), chairman of the Senate Judiciary Committee, said he will seek prompt action on a bill requiring a defendant to prove insanity in order to win an acquittal on grounds of mental illness.

"I'm simply dismayed by this result," Thurmond said of the Hinckley verdict, adding: "There's something basically wrong with the insanity defense."

As the public furor over the verdict mounted, Hinckley was quietly transferred early yesterday morning from the cellblock at the U.S. District Courthouse in Washington, where he was held during his trial, to the army stockade at Fort Meade, Md. Later in the afternoon, Judge Barrington D. Parker ordered that Hinckley be "committed forthwith" to St. Elizabeths Hospital for the mentally ill.

Hinckley arrived at the hospital at 7:35 p.m. yesterday.

Parker directed the hospital staff to examine Hinckley to determine whether he is still mentally ill and whether he is a danger to himself or the community. He ordered the staff to submit its findings to the court, the prosecution and defense lawyers by Aug. 2, and he scheduled a hearing for 10 a.m. on Aug. 9 to determine whether Hinckley is entitled to release.

Each of those steps is required by law as a result of the jury's decision that, on all 13 counts against him, Hinckley was not guilty by reason of insanity.

Parker had earlier scheduled a July 12 hearing on Hinckley's case. It was not clear after yesterday's order whether that hearing would be held or what its purpose would be if it were.

Hinckley's defense lawyers, in a statement, said Hinckley himself "has no current intention" of exercising his legal right to seek release. His parents, JoAnn and John W. Hinckley Sr., said in a separate statement that they, too, will make no attempt to secure their son's freedom "until he has recovered to the point that he is judged to be harmless and responsible."

"We firmly believe that John's longstanding mental disorders were the cause of the tragic events of last year and that he could not have committed such acts unless he were terribly ill," the parents said. They thanked the jury for arriving at the "correct decision."

Hinckley's parents had a brief visit with him in the courthouse cellblock after the jury verdict Monday night. Hinckley showed "no real display of emotion" after the verdict, a source said, and quietly cooperated with deputy U.S. marshals who transported him, and his belongings, to the army stockade at Fort Meade.

Senate and House Republican leaders met at the White House with Reagan yesterday and reported afterward that the president made no comment about the jury's verdict. The other shooting victims, presidential press secretary James Brady, D.C. police officer Thomas K. Delahanty and U.S. Secret Service agent Timothy McCarthy, and their families, also remained silent about the decision.

Treasury Secretary Donald Regan, who, emphasizing he was speaking for himself, said he thought the jury's verdict was "beyond belief."

"Frankly, I'm outraged at that jury decision. I think it's wrong. I think it's not the type of thing that society should condone. I think when a person stalks a leading citizen of this country, shoots him, three of the poeple surrounding him and then goes off scot-free, I think that's absolutely atrocious," Regan said.

White House counselor Edwin Meese told ABC News he was "surprised" by the verdict. But he added, "Our concern has not been with the verdict in this particular case but rather that this case points up what has been a fact for quite some time.

"Many people, legal scholars, people in the criminal justice system, know that something has to be done concerning the law that relates to the insanity defense," Meese said.

House minority leader Rep. Bob Michel (R-Ill.), describing conversations with other House members about the Hinckley verdict, said, "There's a sense of . . . I don't know if outrage is the word. You have to ask the question 'If the president was actually killed would it have changed the minds of those jurors?' "

Not everyone was critical of the jury's decision.

"I canonize them," said Chicago's federal defender Terence F. MacCarthy, chairman of an American Bar Association task force on criminal responsibility. "Can you imagine what's going to happen to those poor people now? They're going to be the scapegoats of the whole thing . . . I admire them . . . they did a very unpopular thing."

Sen. Orrin Hatch, who along with Thurmond supports bills that would sharply curtail the insanity defense, said major changes are needed "not necessarily because the jury is wrong but because the law is wrong."

Attorney General William French Smith, in a rare public comment on a verdict adverse to the prosecution, said yesterday that the Hinckley case "demonstrates again the need for responsible reform in the federal criminal law"--particularly the rules governing the insanity defense.

"There must be an end to the doctrine that allows so many persons to commit crimes of violence, to use confusing procedures to their own advantage, and then to have the door opened for them to return to the society which they victimized," Smith said.

There are at least three bills in the Senate targeting the insanity defense, including Thurmond's so-called Omnibus Violent Crime Act, which is backed by 52 Senate cosponsors and the Reagan administration. A measure, introduced yesterday by Sen. Arlen Specter (R-Pa.), would put the burden of proof on the defendant and narrow the scope of expert psychiatric testimony.

Legal observers said yesterday that congressional action would have limited effect on the use of the insanity defense, since the vast majority of cases in which mental illness is a question are brought in the state courts.

According to the American Bar Association, at least 20 states are considering legislation that would either abolish the insanity defense or adopt various other formulations, such as "guilty but mentally ill." Five states--Michigan, Illinois, Indiana, Georgia and New Mexico--have approved that type of verdict, an ABA spokesman said.

The Idaho legislature, in a move that is certain to face legal challenge, recently eliminated the insanity defense altogether, allowing the judge to consider evidence of mental illness at the time of sentencing.

A spokesman for Specter's office said yesterday that hearings will be held, possibly as early as Thursday, on the bills now before the Senate, a discussion that is certain to be fueled by the verdict in the Hinckley case.

The jurors at Hinckley's trial heard weeks of long and contradictory testimony from a parade of psychiatric experts for the prosecution and the defense about Hinckley's state of mind when he fired on Reagan. After listening to that testimony, the jury had to decide whether as a result of a mental disease or defect, Hinckley was unable to abide by the law or could not appreciate that his acts were wrong.

As is the rule in the federal courts, Parker told the jurors that the burden was on the prosecution to prove that Hinckley was sane. If they failed to do that, Parker told them they were required to find Hinckley "not guilty by reason of insanity."

D.C. law places that burden of proof on the defense in insanity cases. Because there were both federal and local charges against Hinckley, there was a debate early in the trial as to whether the D.C. or the federal standard should apply. Parker ruled in favor of the federal practice.

Hatch said yesterday the bill he proposes, which has been incorporated into the Omnibus Violent Crime Act, would require a defendant to be found sane and responsible for his acts if he "essentially knew what he was doing."

That provision would mean the jury would not be asked to consider the more complex questions put to the Hinckley jury about appreciation of wrongfulness and ability to control conduct. The prosecution would have to prove the defendant had the intent to commit the crime--which it has to do in all criminal cases--but it would not be faced with the more difficult burden of proving a defendant was sane.

A staff member said yesterday that it was the Hinckley verdict that caused Thurmond to become interested in legislation that would shift the burden to the defendant when the insanity defense is raised.

The Specter bill would keep the insanity defense in place but it would shift the burden to the defendant to prove insanity by "clear and convincing evidence." The defendant would have to show that mental disease impaired his understanding of either the nature of his act or its wrongfulness.

In that bill, expert psychiatric testimony would be limited to the doctor's observations of a defendant's behavior. It would preclude psychiatrists from testifying--as they did in the Hinckley case--about their opinions as to whether a defendant was impaired because of mental illness. At Hinckley's trial, a series of those questions were put flatly to the experts on both sides, and they gave flatly contradictory answers.

Legal observers said yesterday they were not surprised that the outcry over the Hinckley verdict had prompted some members of Congress to jump into the debate about the insanity defense, which has long been simmering in the legal community.

"It's going to be irresistible," said Harvard law professor Alan Dershowitz of the burgeoning drive for reform. At the same time, however, Dershowitz praised the jury's verdict as a "remarkable comment on the independence of the American legal system," adding:

"It just couldn't happen anywhere else."