For Terrace Johnson, 15 years old and charged with a double murder, the trial is far in the future and its outcome uncertain. But today he is set to walk into a Prince George's County courtroom and what happens there could have a far more profound effect on how he spends his life than all the judicial proceedings that follow.

Today is not the day for a jury to weigh his guilt or innocence. This is the day when a judge will hear testimony to decide whether Johnson, just out of ninth grade and accused of first fatal shots at two Prince George's patrolmen, is, in the eyes of the law, a child or an adult.

The stakes are high. If tried as an adult and convicted, Johnson could face life in prison. If his case is heard in juvenile court, then, no matter what the outcome, he would be free of the court's jurisdiction when he reaches 21.

A case like Johnson's epitomizes the national debate over how youths charged with violent crimes should be handled - as children in need of rehabilitation or as criminals deserving punishment.

In Maryland there has been a steady march to the judicial bench of youthful figures charged with heinous crimes seeking that determination.

Last April in Anne Arundel County there was Stuart Kreiner, sensitive, vulnerable, often the "odd man out" and emotionally a 12-year-old, the psychiatrists said. He was 16 when he was accused of stabbing three young girls to death in his Southgate neighborhood.

Today there is Johnson, accused of killing policeman Albert M. Claggett IV and James B. Swart as he was being booked at the Hyattsville police station. His lawyers will present doctors' reports and teachers' testimony to show that he should be tried as a juvenile.

Next Monday, Paul Wersick will appear before a Montgomery County judge. Wersick is a small, quiet 15-year-old, who a counselor said had "a history of fantasies about violence" and was not getting the help he needed. He is charged with shooting a county assessor in the head, and is asking to be tried as a juvenile.

Many judges and lawyers in Maryland believe that this is one of the most weighty and perplexing issues a judge must face, as Anne Arundel County Circuit Court Judge E. Mackall Childs can attest.

Childs, weighing the murder of three young girls against the recommendation of two psychiatrists that Stuart Kreiner be tried as a juvenile, ruled that Kreiner should remain in the adult judicial system. "Believe me, I lost a lot of sleep over that case and I still do," said Childs, who stated in his court opinion that the victims' families and the public deserved an open trial rather than a hearing behind the juvenile court's "veil of secrecy."

A myriad of complicated laws, varying from state to state, govern when a youth charged with murder is legally an adult. In Maryland, those between 14 and 17 are charged as adults and then have the opportunity to persuade a Circuit Court judge at a hearing that they should be sent to a juvenile court. Those 13 and younger are charged as juveniles, and though it is possible for a juvenile court judge to order them tried as adults, local prosecutors cannot recall an instance where this happened.

Although no statistics are available on youths actually tried for murder, Maryland State Police statistics show that 43 persons under 18 years old were arrested last year on homicide charges.

Two youths have been arrested in homicides in both Prince George's and Montgomery County this year.

In the legal debate over the juvenile-versus-adult issue in homicide cases, there are those, like Montgomery County Deputy State's Attorney Timothy Clarke, who say, "Any person who has the ability to take another persons's life in a willful, premeditated act should be prosecuted as a adult." Clarke counterpart in Prince George's County, Joseph Sauerwein, asks: "What difference does it make if the finger on the trigger is that of a 15-year-old or a 70-year-old?"

Juvenile law specialist Adrienne Volenik believes it makes a lot of difference, and that each case involving a young person must be looked at individually. Sometimes there is the overriding need to "keep society safe" from an individual, says Volenik, a lawyer with the National Center for Juvenile Justice in St. Louis. But in other cases, Volenik says: "Don't we also have an obligation to say that a child can be rehabilitated? Do we want to write that person off as a total loss at age 15?"

The legal debate goes on, but what does it really mean to a teen-ager charged with murder?

For Sherry Windt, a fragile, brilliant and deeply disturbed 16-year-old Bethesda girl, getting into the juvenile system meant that she served less than a year in jail, although she was later found to have stabbed her mother to death. She also received nearly $90,000 worth of psychiatric treatment while under juvenile court jurisdiction, and last June, less than three years after her mother's death, she was released from a Baltimore psychiatric facility.

For Stuart Kreiner, remaining in the adult system means that he faces life imprisonment after pleading guilty to three murders.

Maryland Circuit Court judges, deciding how a youth shall be tried, take five factors into account: age, mental and physical condition, the child's amendability to treatment in the juvenile system, the nature of the alleged offense and the public safety.

But as one appellate opinion pointed out, the decision "is rarely a matter of easy choice."

For a young person charged with murder, his fate may well depend on the happenstance of geography. In Louisiana, a 15-year-old would be tried as an adult, with no possibility of going to juvenile court, lawyer Volenik says. In Virginia, the same 15-year-old would be charged as a juvenile, and the decision of whether to try him as an adult would be made by a juvenile court judge.

Judge Douglas H. Moore Jr., of the Montgomery County Juvenile Court, believes Virginia's system makes the most sense. He also believes that in some cases it is in the public's interest for a young person accused of murder to be dealt with in juvenile court. "We have more facilities available that would stand a better chance of rehabilitating him. Let's say there is a homicide, with serious mental and emotional problems tied in. There is a serious question of what the adult system has to offer. If he goes to jail, this person will someday be out on parole."

To Judge Childs, there seems to be "no good answer" as things now stand, "when you know these young people . . . can be dumped on the general prison population, subjected to all the abuses we know go on in the institutions. You wonder what the answer is. There is no answer, as far as I'm concerned."