WASHINGTON — Florida's tough prison sentences for juveniles came under scrutiny Monday at the U.S. Supreme Court, as the justices appeared divided over whether locking up teenagers for life constitutes cruel and unusual punishment.

Attorneys for two Florida teenagers who are serving life in prison with no opportunity for parole told the justices that such sentences are unjust to teenagers, who often outgrow their felonious ways.

Florida argued that banning such sentences would undermine the state Legislature's efforts to cut down on serious violent crimes by juveniles.

The court's conservative bloc — Chief Justice John G. Roberts and Justices Antonin Scalia and Samuel Alito — seemed reluctant to embrace an outright ban on such sentences, suggesting instead that judges take factors such as age into account during sentencing.

"Your client — his crime is horrendously violent," Roberts said to Bryan Stevenson, an attorney for Joe Sullivan, who was convicted of raping an elderly woman when he was 13. "At the same time, he is much younger than in the typical case. And it seems to me that requiring ... consideration of his age avoids all these line-drawing problems."

However, Bryan Gowdy, an attorney for Terrance Jamar Graham, who was convicted of armed robberies when he was 16 and 17, argued that a ban on sentences of life without a chance for parole would be more effective than a case-by-case review, because "we can't tell which adolescents are going to change and which aren't."

"It needs to happen later," the Jacksonville, Fla., attorney told the justices, speaking of decisions about parole. "Once he has matured, once he's reached past adulthood."

Gowdy and Stevenson noted that in a 2005 ruling, the high court prevented those younger than 18 from being sentenced to death for their crimes because young offenders are more easily swayed and lack the judgment of adults. Life without parole, Stevenson argued, is comparable to a death sentence.

"To say to any child of 13 that you are only fit to die in prison is cruel," he said.

The author of the 2005 ruling, Justice Anthony Kennedy, is considered a swing vote on the court, but he gave few clues Monday as to his thinking, asking at one point, "Why does a juvenile have a constitutional right to hope, but an adult does not?"

He also pressed Florida Solicitor General Scott Makar on why the state wants to keep juvenile offenders behind bars.

"What is the state's interest in keeping the defendant in custody for the rest of his life if he has been rehabilitated and is no longer a real danger?" Kennedy asked.

Makar argued that enacting a ban would go against states, such as Florida, that have eliminated parole and have chosen to enact tough laws against violent juvenile offenders.

He told the court that 99 out of 100 juvenile offenders don't end up in adult court and that judges have the discretion to sentence for age.

Justice Ruth Bader Ginsburg said, however, that the judge in the Graham case had "surprised everyone in the courtroom" with the sentence of life without parole, going "far beyond" the 30 years prosecutors had recommended.

Makar said there were no Florida inmates under 13 with such sentences, but Justice Sonia Sotomayor asked whether under state law "a 5-year-old could be put away for life?"

"That is theoretical," Makar acknowledged. "We would hope that the system would not allow that to occur."

Still, several justices appeared unconvinced that such prison terms aren't appropriate for extremely violent crimes that fall short of murder.

Alito recited details of several cases "so horrible that I couldn't have imagined them," including one in which a juvenile offender had raped an 8-year-old, "burying her alive."

Alito also suggested that a ban on such sentences "would deprive the state from reaching the judgment that there are some juveniles, some individuals, who are short of their 18th birthday, who deserve life imprisonment without parole."

The justices heard two hours of arguments stemming from the two cases in Florida, which defense attorneys said led the nation in the number of inmates serving life without parole for crimes committed while they were teenagers.

The defense lawyers noted that although more than 30 states permit such sentences, they're rarely imposed, suggesting a "societal consensus" that such punishments are unusually harsh.

Roberts, however, suggested that such sentences are used rarely because there's "strong evidence that they appreciate the gravity of the sentence in the particular circumstances of juveniles and therefore only impose it rarely."

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