WASHINGTON — A seemingly divided Supreme Court wrestled Monday with whether teenagers can be locked away forever for their crimes.

The question arose in two cases involving Florida men who are serving life prison terms with no chance of parole for crimes they committed as teenagers. Their lawyers argue that the sentences for people so young are cruel and unusual, in violation of the Constitution, because young people have greater capacity to change.

Justice Anthony Kennedy wrote the Supreme Court opinion four years ago that ruled out the death penalty for people under 18, judging them less responsible than adults. So most eyes were on him Monday as the court considered whether to extend that rationale to life without parole sentences.

But Kennedy offered little hint of his position, at one point suggesting it might be difficult to distinguish between juveniles and adults in cases that do not involve the death penalty.

"Why does a juvenile have a constitutional right to hope, but an adult does not?" he asked.

Justice Ruth Bader Ginsburg provided a possible answer, wondering whether teenagers can be accurately evaluated at the time they are sentenced. It may be possible that only after some years have passed that the state can determine, "Has this person overcome those youthful disabilities?" she said.

On the other side of the issue, Justice Samuel Alito questioned whether every last juvenile offender had to be given a second chance. "Some of the actual cases in which this sentence has been imposed in Florida involve factual situations that are so horrible that I couldn't have imagined them if I hadn't actually seen them," Alito said, recounting two that involved the rape of children.

In the two cases before the court, Joe Sullivan was sent away for life for raping an elderly woman when he was 13 and Terrance Graham was implicated in armed robberies when he was 16 and 17.

Graham, now 22, and Sullivan, now 34, are in Florida prisons, which hold more than 70 percent of juvenile defendants locked up for life for crimes other than homicide.

The justices could distinguish between the two based on the difference in their ages at the time of the crimes: It could rule that someone as young as Sullivan was must eventually be considered for parole without granting Graham any relief from his sentence.

Sullivan's lawyer, Bryan Stevenson, stated his basic argument simply: "To say to any child of 13 that you are only fit to die in prison is cruel." Sullivan would be resentenced to 40 years in prison if he were to win his case at the high court, he said.

Kennedy's opinion in 2005 was rooted in two principles — that death is different from other punishments and that children are less culpable than adults.

Following that ruling, Stevenson noted that juveniles on death row in Florida — all convicted of murder — "got a better sentence than Joe Sullivan," life prison terms with the possibility of parole.