THIS PAST WEEK, Texas executed a prisoner named Charles Rumbaugh, Jr. Rumbaugh was the 40th person to be put to death in the Southern states since the death penalty began its resurgence here in earnest two years ago. By now, such executions are hardly news. But last Wednesday's execution marked a legal watershed of sorts, because Charles Rumbaugh was put to death for a crime that he committed when he was just 17 years old. Until last week, it had been more than 20 years since any American had been executed for a crime committed while he or she was a minor.

Charles Rumbaugh could not have been sentenced to death if he had committed his crime in South Africa, Libya, Iraq, the Soviet Union or China, instead of in Texas. The laws of each of those countries forbid the infliction of the death penalty on anyone who was under 18 at the time of his crime. So does the International Covenant on Civil and Political Rights, which President Carter signed in 1978 (but which the Senate has yet to ratify).

But the state of Texas uses 16 as its age limit for the death penalty, and 26 other American states impose even lower age limitations -- or no age limits at all -- on who may be executed. Just this year, the Maryland state senate defeated a bill to establish 18 as the minimum age for a death sentence: Similar efforts have fared no better in other states. As a result, more than 30 inmates who were 17, 16, and even 15 when they committed the murder which put them there await execution on this country's death rows. And this number is gradually increasing.

Rumbaugh was not the youngest person to be put to death in this century. That distinction belongs to a 14-year-old black boy named George Junius Stinney Jr., who was executed on June 16, 1944. Stinney was electrocuted less than two months after being convicted of the murder of an 11-year- old white girl in Clarendon County, S.C. At the time of his death, he was 5 feet 1 inch tall and weighed 95 pounds.

George Stinney's case raised no great legal questions for the judicial system of that time. Indeed, it raised no legal questions at all, because his death sentence was never appealed to any court, and now the county court records of the case have been lost.

Because it seemed safe to assume until recently that no one as young as Stinney could possibly ever be sentenced to death again in this country, there was little reason to recall the details of his obscure and long-forgotten case. But now that the United States has resumed executing people for crimes committed while they were juveniles, we might consider what, if anything, the crime and punishment of George Junius Stinney Jr. has to teach us now.

Betty June Binnicker and Mary Emma Thames, aged 11 and 8, had ridden Betty June's biccle to the edge of the small lumbermill town of Alcolu that spring afternoon to pick wildflowers. They didn't come home that night, and the next morning a search party of lumbermen found their bodies in a water-filled ditch. They had both been killed by blows to the head. Within a few hours, Stinney, the eldest child of a black sawmill worker, was arrested.

Eventually he confessed to having killed the girls, and helped the police recover a railroad spike which, he said, had been the murder weapon. He was secreted out of the county just ahead of a lynching party of white lumbermill workers and merchants. That same day, the mill owner told Stinney's father to leave Alcolu, and Stinney's entire family left their company-owned home and boarded a northbound train with what they could carry, never to return.

Stinney was brought back to Clarendon County to stand trial on April 24, 1944, just a month after his arrest.

A special term of court had been summoned, and the presiding judge had appointed a 31-year-old local lawyer and fledgling politician named Charles Plowden as Stinney's defense counsel.

That spring, Plowden was preparing to run for the statehouse after losing a bid for the state senate in the previous election, and an appointment to so controversial a case could not have been welcome. The case looked no easier after Plowden met his client: Stinney admitted his guilt, and Plowden saw no defense. He also decided that there was no need for a psychiatric evaluation, and none was performed.

As the trial began, the Clarendon County Courthouse was overrun with a crowd estimated by the local newspaper at 1,500, several times the capacity of the courtroom. The crowd overflowed into the hallway, down the stairs and onto the courthouse grounds. Despite the huge crowd (or possibly because of it), Plowden made no request to move the trial to another county, and a jury of 12 white men was selected before the midday recess. Testimony began at 2:30 that afternoon, and by midafternoon, the prosecution had presented its entire case.

The main evidence against Stinney was his confession: according to the police, the boy had admitted that he'd seen the girls while he was minding the Stinney family cow, and that he'd followed them into the woods. Stinney admitted that he'd tried unsuccessfully to rape the older girl, and that he'd beaten both children with a railroad spike that had been lying near the track. The last piece of evidence presented was a birth certificate showing that Stinney had been born on Oct. 21, 1929, and that he was therefore 14 years old -- the traditionally accepted age of criminal responsibility.

The defense offered no evidence. The local newspaper reporter described Stinney, who was dressed in a faded blue shirt and jeans, as looking "unconcerned" as he sat through the testimony. To Roston Stukes, a white Alcolu merchant who attended the trial, he "looked more like he was more scared to death."

"The boy looked like he was in a dazed condition," Stukes recalls. "He seemed like he didn't really realize the seriousness of the crime that he'd committed."

The jury retired at five minutes before 5 to deliberate. Ten minutes later it returned with its verdict: guilty, with no recommendation of mercy.

According to the local newspaper reporter, Stinney was "nervous and slightly excited" when he was ordered to rise for sentencing, and bit his finger while he stood facing the judge. He had nothing to say. The judge sentenced him to be electrocuted at the state penitentiary in Columbia on June 16, 1944.

The execution would have been automatically stayed for at least a year if Plowden had filed a one-sentence notice of appeal, and then appealed the case to the state Supreme Court. But when Stinney was led out the courtroom that Monday afternoon after the death sentence was imposed, he was on his own. Plowden never saw the boy from that moment on, never spoke to any member of his family and never advised Stinney or his parents that he had a right to appeal.

"There was nothing to appeal on," Plowden recalled in an interview two years ago. And, he added, Stinney's family had no money to pay for an appeal.

With Plowden's withdrawal from Stinney's case, there was nothing left to do but wait. The Stinney family had no resources or understanding of the legal system: Stinney's younger sister Kathrine, now a schoolteacher in Passaic, N. J., remembers that all her mother could do during those weeks was pray. With no appeal filed, only an order of clemency from Gov. Olin D. Johnston could stop the execution.

Stinney's trial and sentence had attracted little attention beyond Clarendon County, and none at all outside of South Carolina. But as the date of his execution neared, Johnston received pleas from several local NAACP chapters, ministers' associations and labor unions urging that George's sentence be commuted to life imprisonment on account of his age.

Then, on June 12, the Associated Press ran a story about the impending execution. There followed several hundred letters and telegrams from throughout South Carolina and the country, the large majority in support of clemency.

A few supported the governor's announced intention to allow the execution to proceed: E. P. Thomas of Austin, Tex., wired that he was "SURE GLAD TO HEAR OF YOUR DECISION REGARDING NIGGER STINNEY." But most of the telegrams and letters urged Johnston to commute the death sentence. Many of the letters alluded to the war: as one telegram insisted, "CHILD EXECUTION IS ONLY FOR HITLER."

One letter from Myrtle Beach, S.C., said simply:

"Enough murder and carnage in this world at present, without the state of South Carolina joining in by killing a 14-year-old boy.

An Atlanta man wired that "WHOLE NATION WOULD BE SHOCKED BY EXECUTION OF A CHILD." Like many others, George Murphy of Ridgeway, S.C., reminded Johnston of the lenient sentence imposed in a recent a Parris Island, S.C., case involving a rape-murder by a 16-year old white boy:

"I am a White Man, I believe in the right thing among the white or colored. Now I am pleading with you for the life of the little Negro boy age 14 that kill, the two little white girls. They gave the white boy that kill the little girl in Parris Island 20 years in prison. A sentence in prison would be fair for the Negro boy. Please Governor try to save this boys life."

But Johnston's mind was already made up. Charles Plowden was not the only one facing a primary election fight in July: Johnston had challenged South Carolina's veteran segregationist Sen. "Cotton Ed" Smith in the Democratic primary for United States Senate, and any hint of vacillation on the racial issue could be costly.

Meanwhile Stinney waited in a small holding cell just a few feet from the death chamber. On June 13, prison officials interviewed Stinney in the presence of a reporter for The Columbia Record. Stinney was reluctant to speak at first, but he eventually repeated his confession. He also told the officials that he had been finishing the seventh grade when he'd been arrested. "He appeared nertnd what was happening to him. He was struck by the fact that Stinney appeared too small for the electric chair.

"It had a lot of effect on me," the veteran state police lieutenant says now. "For a long time I turned against electrocution, period. I'm not that way today. I think the death penalty is proper in its place . . . . But I don't think that a 14-year-old should be electrocuted. I didn't then, and I don't today."

Betty June Binnicker's father and older brother Raymond were also at the prison that morning to watch the execution. Both are dead now. Vermelle Tucker, Betty June's older sister, recalls that her father had looked forward to seeing Stinney die. But when her father and brother returned, neither of them was eager to talk about what he had seen, and Raymond refused to say anything at all.

"I think it really worried him," Vermelle recalled 40 years later. "Because if it hadn't, I think he'd have talked about it. I think he thought that he'd feel real relieved about it after, about watching the little boy get killed, but after it happened, I really don't think he felt that way."

No one quite as young as George Stinney had been executed before in this century, and no one ever would be again. But executions of prisoners who were 16 and 17 at the time of their crimes continued until the mid-1960s, and now, with Charles Rumbaugh's execution in Texas last week, they have resumed. It may be that the execution of a boy quite as young as 14 couldn't happen today. But it "couldn't happen" in 1944, either: as the letters of protest to Johnston made clear, the execution of so young a child was unthinkable to many people at that time, and had the political climate been not been different in that spring of 1944, George Stinney's sentence would likely have been commuted. Stinney just slipped between the cracks of a legal system that, then as now, almost never executes children.

Of course, in one respect an execution like George Stinney's is certain never to recur: the teen-agers on death row today won't be executed until they're grown to adulthood while appealing their sentences. Some of these men may bear little resemblance, by the time they are put to death, to the teen- agers who committed their crimes.

This is certainly a difference between today's death penalty system and the one that took Stinney's life.

But the change is only cosmetic. What matters isn't how responsible someone is when we execute him, but how responsible he was when he did what we're executing him for. It wouldn't have made Stinney's sentence any fairer to have locked him in a cell until the boy who committed murder had grown into a man of 21 or 24, and to have executed him only then.

It might seem at first that what happened to Stinney reflects only the judicial mores of the Old South. But the people who tried and executed Stinney were not monsters. They were ordinary people reacting to a horrible crime: Their sympathies lay with the victims and the grief-stricken parents rather than with the killer.

The feelings that motivated them are familiar today as Americans seek ever more drastic responses to violent crime. What was unusual about Stinney's case wasn't the anger of the community which tried and condemned him, but the fact that the community's anger encountered no restraint.

That's why democracies have laws that impose absolute limits on what government can and can't do to punish individuals. In calm times, these laws don't appear to be needed: The limits on punishment are embedded in our society's basic sense of decency, and don't have to be enforced by court orders. But from time to time a particular crime tempts us to cross the line from justice to cruelty. And when that happens, there will usually be some perfectly sensible- sounding arguments in favor of cruelty.

The supporters of society's right to use the death penalty against youthful prisoners argue that the law should not be rigid. Some juvenile murderers are more mature than others, they say. Some are more dangerous than others. No matter that the law says that all juveniles are too immature to vote or to sign for a loan: Whether they're too immature to be executed, the argument goes, is something that we ought to let a judge or jury decide, one kid at a time.

Terrible crimes sometimes give this argument a certain appeal. Such crimes need to be punished, and punished severely. Society has the right to imprison juvenile offenders, for life if need be. But there is only one way to ensure that we will never again reenact the demoralizing spectacle of the execution of George Stinney. And that is to draw an age limit for the death penalty that admits of no exceptions. Most of the world's countries that still use capital punishment have drawn that line at 18. So should we.