Death penalty statutes should be brought into line with other laws that treat juveniles differently, a lawyer representing a murderer sentenced to death for a crime he committed at age 16 told the Supreme Court Monday.

The comments came as the court heard oral arguments in two cases dealing with whether the court should set a minimum age for capital punishment, a question the court has so far been unable to answer.Nancy McKerrow, representing a death row prisoner from Missouri who was 16 at the time of his crime, told the court that "children are not small adults. Even the most mature adult is still a child."

She said that in Missouri a 16-year-old is not eligible to vote, sit on a jury or even witness an execution. She said giving the death penalty to those under age 18 violates the Constitution's Eighth Amendment ban on cruel and unusual punishment.

Frank Heft, representing a convicted killer from Kentucky who was 17 at the time of his crime, said the death penalty has no deterrent value for juveniles, who he said have no fear of death.

Yet those arguing in favor of retaining the option to sentence those under 18 to death said the sentences are meted out on a case-by-case basis and the individual level of maturity is considered.

John Morris, representing the state of Missouri, said the criminals are "sentenced to death for what they did, not what they are."

Frederic Cowan, the attorney general of Kentucky, said the argument that people become sophisticated, mature and responsible adults at age 18 "flies in the face of common sense." He said people develop at different levels and that maturity and sophistication exist on both sides of 18.

He said setting 18 as the minimum would "guarantee injustice" and set up a system where two people involved in a murder could get different sentences solely on the basis of birth date.

The cases present the court with the question of whether ordering the execution of a 16- or 17-year-old criminal violates the Eighth Amendment ban on cruel and unusual punishment.

The court decided to take on the issue on the last day of its 1987-88 term just a day after striking down state laws that allow the death penalty for juveniles who are 15 or younger.