Like presidential assailant John W. Hinckley Jr., Howard Lawrence Merle was committed to St. Elizabeths Hospital for an indefinite period after being found not guilty of a felony crime by reason of insanity. Now, 10 years after he was confined, government prosecutors say Merle's commitment was a mistake.

A public defender raised questions about Merle's case after discovering that, unlike Hinckley, Merle did not want to use the insanity defense. The court, over his objections, did it for him.

In 1962, the Supreme Court ruled that if a judge imposed an insanity defense on a defendant, that person is entitled to a civil commitment proceeding, including a separate jury trial, before being confined to a mental institution.

In Merle's case, the court followed the normal procedure for a trial in which a defendant successfully pleads not guilty by reason of insanity, ordering him committed as soon as the jury's verdict was returned.

Government prosecutors recently acknowledged in court documents that Merle's "mandatory commitment is illegal." Next week city mental health commissioners are scheduled to hear arguments over whether Merle, who could have faced life in prison if he had been convicted, should be confined to a mental hospital at all.

The dispute over his commitment rests on a technical point of law that points up the tangled legal questions involved when a defendant's culpability is measured by his state of mind. In this case, the ultimate issue is who--Merle or the government--must bear the burden of proving Merle's mental condition, and who--psychiatrists or the court--should decide when he goes free.

Under criminal commitment, defendants are confined indefinitely until they can satisfy the court that they no longer pose a danger to themselves or the community. Under civil procedures, the burden shifts to the government to show that a mental illness and danger exist, and hospital staff members decide when a patient has recovered enough to be released.

Merle, 44, was brought to trial in U.S. District Court in 1972 for raping an 11-year-old girl he said was helping him sell some old clothes. He maintained his innocence.

Hospital psychiatrists, according to court documents, initially found him incompetent to stand trial. After a period of treatment at St. Elizabeths, Merle was ruled competent to be tried although he was diagnosed as schizophrenic, the records say.

According to trial transcripts, Merle's court-appointed defense attorney, the prosecutor and Judge Gerhard A. Gesell all grappled with a dilemma that one Justice Department official described as "infrequent but not rare:" whether to raise an insanity defense even though Merle objected to it.

"Mr. Merle from day one appeared to be so disturbed, being in the courtroom and not knowing which way was up, there was a question of competency right off," said Merle's current public defender, Harry Fulton.

According to Justice Department officials, lower court rulings before and since the 1962 Supreme Court decision place on judges an obligation to raise the insanity defense when a mentally impaired defendant refuses to do so himself. Gesell did just that, ruled Merle was not guilty by reason of insanity and then ordered him confined to St. Elizabeths.

Gesell declined to comment on the case.

In the 10 years of his confinement, according to letters from St. Elizabeths officials contained in the court record, Merle has concealed weapons, escaped at least three times, been arrested for streaking, accosted staff with obscenities and threats, endangered his own life by mixing alcohol with his medication, adopted faith healing and written Gesell and other federal judges a continuous stream of briefs seeking his freedom.

Recently, Fulton asked Gesell to terminate Merle's commitment. Following a government reply in which federal prosecutors conceded that Merle's "mandatory commitment is illegal," Gesell last month gave federal authorities 30 days to seek a civil commitment in D.C. Superior Court.

Federal prosecutors, who declined to discuss Merle's case on the record, have petitioned the D.C. Commission on Mental Health to have Merle civilly committed. The commission, which set a hearing for July 1, makes commitment recommendations to the court.

A civil suit filed by Merle in U.S. District Court against Gesell and Merle's former attorney was dismissed last week by Judge John Garrett Penn, who ruled that the suit presented "no facts on which to grant relief."

Already, Merle's life has changed significantly. Since Gesell's order setting the original commitment aside, he has been moved into a minimum security ward. Fulton said Merle "has not shown any of the behavior that triggered his incarceration in 1971."

A certificate from hospital psychiatrists accompanying the government's petition says that while Merle's "judgment and insight are questionable," he is "in no acute distress from mental illness" and recommends he be placed under out-patient care.