Donald Lang, an illiterate deaf-mute, has spent almost all of the past 15 years locked up in mental hospitals or jails in a seemingly interminable legal limbo.

He has been charged with two separate murders, so he cannot be released until he is tried.

But he cannot be tried because he does not know sign language and cannot defend himself.

And he cannot be taught sign language, apparently, as long as he is locked up. There are no classes in the Cook County Jail.

Lang became a symbol of the inflexibility of the legal system when a book, "Dummy," was published in 1974 about his life. A television movie based on the book was shown last year.

Last month, the case came before the U.S. Supreme Court, which declined to consider it. Theoretically, that should have resolved something. It appears that it did not. Lang is still in limbo.

The various lawyers in the case are now engaged in another lengthy court battle. Lang is accused of murdering two prostitutes in two separate incidents. The charges in the first murder eventually were dismissed and the state's attorney wants to proceed to trial on the second murder charge. aThe county public defender for Lang is trying to get the second charge dropped. A second set of lawyers for Lang, retained by his brother, is trying to get the public defender dropped.

"Everything is terribly confused again," said Christine Bremer, a special assistant Illinois attorney general. "The infighting is beyond belief."

Four years ago, while Lang temporarily was confined in a mental hospital, he received his first systematic instruction in sign language and made extraordinary progress, according to his teacher.

But because he was not mentally ill, state mental health authorities insisted the law required that he leave. Lang was transferred to the Cook County Jail.

By all accounts, he has forgotten most of what he had learned. However, he still can communicate one thought to his lawyers: a house drawn in the air with the index finger.

Lang is neither mentally ill nor retarded. This is the conclusion of teams of doctors who had studied him while he was in the Illinois State Psychiatric Institute.

He had been employed on truck loading docks in Chicago before his first arrest. Afterward, while in custody, there was no evidence that he was inclined toward violent or even particularly hostile behavior against those around him.

He has reasonable intelligence. Donald Paull, Lang's public defender, who is also a clinical psychologist, says that special tests have placed Lang's I.Q. at about 128 -- normal to bright.

His problem was that he never was taught sign language. Instead, his sign language teacher, Candy Haight, said, he engaged in "verbal behavior," struggling to imitate speech he had never heard and coming forth only with unintelligible noises.

"The first thing I had to do was let him know I didn't understand him," Haight said. "I absolutely and totally ignored him" when he made the noises. "I simply did not respond.

"I would go and stand in a corner and cover my ears and turn my back."

"It was frustrating for him," she said, but he learned. "He became capable, for the first time, of expressing his feelings."

Haight described Lang as a "warm and gentle" man until he becomes agitated.

When he was agitated, she said, "he became very deaf again."

His legal tangle -- the seemingly endless series of lawyers, court appearances, examinations and consultations that Lang signified by holding up his right hand as if taking the courtroom oath -- always agitated him.

His marathon encounter with the law began in 1965, when he was arrested and charged with the murder of the first prostitute.

He subsequently was committed to a mental hospital, which determined that he was unlikely ever to become fit for trial because sign language training had been unsuccessful.

While officials and the courts debated whether to bring him to trial anyway, a principal witness died and the state dismissed the charges. Lang was freed in February 1971.

Five months later, another prostitute was murdered, beaten severely on the head and stuffed in a closet.Lang was arrested and charged with the crime.

This time, Lang was tried and convicted. Included in the evidence was a drawing he made during his interrogation. A woman was depicted with an "X" drawn over her. Authorities interpreted this as a crude form of confession.

His lawyers, demonstrating the extraordinary pitfalls of such interpretations with a noncommunicative defendant, pointed out that it could just as easily be Lang's description of something he witnessed, rather than something he did.

In 1975, an appellate court reversed the conviction.

Then Lang had to undergo a proceeding to determine his potential for retrail. He was assigned to the Illinois Department of Mental Health for treatment and confined in the psychiatric institute, where Candy Haight began teaching him.

Teaching sign language to an adult whose habits are ingrained ordinarily is difficult, Haight said. In Lang's case, she also was concerned that establishing rapport would be difficult if he had trouble relating to women.

Both problems were overcome, Haight said, and Lang absorbed at least 200 formal signs, most of them relating to his surroundings and circumstances.

"I would take something we were actually involved in, "she recalled." I would have a cigarette out. He would want one. I would pick up the cigarette lighter and at the same time show him the sign for the word, 'lighter,' represented by a hand gesture imitating a flicking action."

Could he have been made fit for trial in this way?

"I really don't know" Haight replied. "But I always thought he should be given a chance."

Because the Department of Mental Health concluded that Lang was not afflicted with a mental disorder, it had the courts discharge him to the Cook County Jail in October 1977.

Illiterate deaf-mutes charged with serious crimes are few and far between. Illinois law -- not without justification -- makes no provision for them.

"Legislators didn't even conceive of a situation like this," said Sy DuBow, legal director of the National Center for the Law and the Deaf at Gallaudet College in Washington, D.C. "So people say, 'Well, there's nothing we can do if the legislature didn't provide for it.' There were so many legal minds involved in this case, so many people, yet they went back to square one."

One special assistant attorney general Bremer, now says she wishes "in hindsight" that the state had quietly continued Lang's training in the hospital.

"We probably should have considered that," she said. "All of us would have gotten by a lot of crap if we had just kept him."

Instead, the Department of Mental Health resisted in the courts all efforts to include it in the training of Donald Lang. When the Illinois court ruled that Lang could be discharged to the Cook County Jail, for example, the court also ordered the department to develop training programs for Lang.

The department appealed all the way to the U.S. Supreme court, which three weeks ago declined to consider the case.

The appeal took three years.By the time it arrived at the Supreme Court, the case had, as Bremer said, little or nothing to do with Donald Lang. It centered instead on broader issues of state law and involuntary commitment.

But Lang was confined throughout, and remains confined.