Several Supreme Court justices indicated yesterday that it may be difficult for them to definitely answer whether or when lethal injections violate the Constitution's protection from cruel and unusual punishment.

The morning arguments before the court came in a Kentucky case that has led to a halt to executions across the country. A lawyer arguing on behalf of two Kentucky death row inmates told the court that the three-drug protocol used by states and the federal government carries the potential to cause unnecessary and excruciating pain during executions.

"The risk here is real. That is why in the state of Kentucky it is unlawful to euthanize animals in the way it carries out its executions," said Washington lawyer Donald B. Verrilli Jr., who is representing Ralph Baze and Thomas Bowling in the case, Baze v. Rees.

The main problem, the court was told, is the second drug in the sequence, which paralyzes the muscles. If the inmate is not properly anesthetized, the paralytic could mask whether the condemned is in tortuous pain.

Justice John Paul Stevens said he was "deeply troubled" by the use of the second drug, but that there was nothing in the record in the Kentucky case that raised the issue in a way for the Supreme Court to make a definitive ruling. Kentucky, he said, seemed to have done a good job of administering the drugs in the state's only execution by lethal injection.

Justices David Souter and Stephen Breyer also said it might be better to send the case back to lower courts for a comparative analysis of whether the three-drug process carries more risk than an alternative, which uses only a massive dose of a barbiturate.