Convicted murderer and rapist John Kevin Johnson was saved from death by a single Prince George's County juror yesterday. After deliberating 15 hours through the night, a tired and unkempt jury announced it was "hopelessly deadlocked" and could not decide unanimously to condemn Johnson to the gas chamber.

Circuit Judge Audrey E. Melbourne then imposed a life sentence on Johnson, as required by Maryland law.

As she spoke, the mother and twin sister of Arlene Flowers, the 13-year-old Southeast Washington girl Johnson abducted, raped and killed with a blast from a sawed-off shotgun, burst into tears.

The courtroom in Upper Marlboro was crowded with more than 100 people, many of them backers of stiff anticrime measures proposed as the result of a furor over the sentence given two men who were convicted last month of raping and murdering a college honor student. Those men drew life sentences that will permit them to become eligible for parole in a dozen years.

It is uncertain how much time Johnson, a 27-year-old farm laborer and mechanic from Accokeek, will have to serve in prison before he is eligible for consideration under the state's parole system. The life sentence imposed yesterday was for murdering the girl. He still faces sentencing for rape, another sexual assault, abduction, kidnaping, armed robbery, assault with a deadly weapon and a second weapons offense in the same case. He could receive additional life terms for each of the first three of those offenses.

If Melbourne decides to impose consecutive rather than concurrent sentences, Johnson's parole eligibility could be delayed for decades. Sentencing is scheduled for Friday.

The judges in the trial of the two men who killed Frostburg State College student Stephanie Ann Roper said they should serve concurrent life terms, and in such cases the possibility of parole comes after 12 years.

Defense and prosecuting attorneys in Johnson's trial said it was the question of parole that caused the jury, with 11 of its members favoring death, to deadlock yesterday. The same jury had earlier convicted Johnson, and the only question before it was whether he should be put to death.

Assistant Prince George's State's Attorney David Simpson said one juror maintained that Johnson did not "pose a future threat to society" -- a point the jurors were required by law to consider -- because he would be spending the rest of his life behind bars. The other 11 jurors apparently considered the possibility of parole and felt Johnson could pose a threat, Simpson said.

The jurors agreed among themselves not to discuss their deliberations publicly. One juror, interviewed at home, said all the jurors felt "just a deep sense of responsibility." Asked to comment on the outcome, this juror, who declined to be identified, said, "We have done our job."

Maryland juries must decide there are "aggravating circumstances" in order to sentence a murderer to death. In the Johnson case, the prosecutor offered only one: that the murder was committed during the commission of the felony crimes of rape and robbery.

If a jury decides that aggravating circumstances exist, it then weighs them against "mitigating circumstances" suggested by the defense or by the jury itself, that may place the defendant in a more favorable light. In this case, Johnson's attorneys argued as a mitigating circumstance that he did not pose a future threat to society. They told the jury that life imprisonment would be punishment enough and that Johnson stood no chance of being paroled before he dies.

While every juror agreed the aggravating circumstance existed, Simpson said, "one person believed the mitigating circumstances outweighed the aggravating circumstances."

The head of the Maryland Parole Commission had testified that there was at least a remote possibility that prisoners serving life sentences could be paroled after 11 1/2 years. According to Simpson, the dissenting juror had no strong opposition to the death penalty itself, but argued that the jury was obligated to assume that all life sentences lasted for life.

Simpson, who pressed for the death sentence, complained after the jurors left the courthouse yesterday that they were forced to "make a determination of complex law in a highly emotionally charged atmosphere."

Defense attorney Edward Camus said the one juror who refused to go along with a death penalty "made the right decision."

Darlene Perry, Johnson's second defense lawyer, burst into tears at the sentence. She said "Kevin is delighted" that he was given a life sentence, rather than death.

Arlene Flowers' 26-year-old brother Morell said his family had hoped Johnson would be sentenced to die. "It didn't come out," he said after the sentencing. "In a way, it seems like another blow because it didn't turn out to meet our expectations. It's going to be difficult to eventually adjust to this verdict."

Johnson showed no emotion as Judge Melbourne sentenced him to life in prison at 9:45 yesterday morning. Several times throughout Tuesday night he was taken, bleary eyed, before Melbourne, as defense attorneys attempted unsuccessfully to persuade her to dismiss the jury for failing to make a decision in a "reasonable time." Sheriff's deputies said that between these appearances, while the jurors deliberated and lawyers paced the corridors, Johnson was sleeping in the small courthouse lock-up.

Defense attorney Camus said he will consider appeals to Johnson's convictions after Friday's sentencing. Prosecutor Simpson said he will ask Melbourne to impose the maximum sentences on all charges.