WASHINGTON — Supreme Court justices engaged in an impassioned debate Wednesday about capital punishment ”“ part of arguments over a single drug that has been used in several botched executions.

The justices heard arguments over the plea of death row inmates in Oklahoma to outlaw the sedative midazolam. They say it is ineffective in preventing searing pain from the other drugs used in lethal injections.

But the hour-plus session featured broader complaints from conservative justices that death penalty opponents are waging what Justice Samuel Alito called a “guerrilla war” against executions by working to limit the supply of more effective drugs.

Among the court’s liberals, Justice Elena Kagan said the way states carry out most executions amounts to having prisoners “burned alive from the inside.”

The unusually combative words came on the court’s last argument day until the fall, and a year to the day after a problematic execution in Oklahoma gave rise to a lawsuit from death row inmates over the use of midazolam.

The outcome itself could turn on the rather narrow question involving the discretion of the federal trial judge who initially heard the lawsuit. He ruled against the inmates, and a unanimous three-judge panel of the federal appeals court in Denver affirmed that ruling.

But justices on both sides gave voice to larger concerns on Wednesday.

“There are other ways to kill people, regrettably, that are painless,” Justice Sonia Sotomayor said.

Justice Antonin Scalia said more effective drugs have been “rendered unavailable by the abolitionist movement.”

The Supreme Court’s involvement in the case began with an unusually public disagreement among the justices over executions.

The court refused to block inmate Charles Warner’s execution in January over the objection of the four liberal justices. In a strongly worded dissent for the four, Sotomayor said, “The questions before us are especially important now, given states’ increasing reliance on new and scientifically untested methods of execution.”

Eight days later, the justices agreed to hear the case of three other Oklahoma prisoners. One possible reason for the different outcomes in what cases to accept is that it takes just four votes among the nine justices to agree to hear a case, but five votes to place a hold on an execution.

Since the January decision to hear the three prisoners’ case, the justices have not prevented other executions from moving forward. Sotomayor and Justices Stephen Breyer, Ruth Bader Ginsburg and Elena Kagan have voted to stop some but not all of those nine executions, which have been carried out in Texas, Missouri and Georgia.

In 2008, the court upheld Kentucky’s use of a three-drug execution method that employed a barbiturate as the first drug, intended to render the inmate unconscious.

But because of problems obtaining drugs, no state uses the precise combination at issue in the earlier Supreme Court case.