Litigation challenging the constitutionality of lethal injection is spotlighting growing evidence that condemned inmates might not be properly anesthetized and therefore experience excruciating pain during executions.

Although lethal injection has become the predominant method of execution around the U.S., it initially was adopted three decades ago without scientific or medical studies, on the recommendation of an Oklahoma state legislator who wanted a more humane procedure.

Since then, objections have arisen in many of the 37 other states that adapted Oklahoma's procedures.

While some death penalty proponents are offended that the state is obliged to limit inmates' suffering during execution, the U.S. Supreme Court in its 1976 decision reinstating the death penalty cautioned that officials must avoid "the unnecessary and wanton infliction of pain."

The problem with the three-stage lethal injection drug procedure is that it may mask rather than prevent pain, critics contend.

The first drug, the sedative sodium thiopental, is meant to deaden pain; the second, a paralytic, to freeze a prisoner and the third, potassium chloride, to stop the heart.

However, sedative dosages, especially as administered by untrained prison personnel, have been found inadequate to anesthetize inmates. Meanwhile, the paralytic drug prevents them from expressing the intense pain of the heart-stopping chemical.

In a study to be released today, Human Rights Watch reported more than a dozen executions in which inmates appeared to have suffered.

In North Carolina

For example, in North Carolina in 2003, a prisoner started to convulse, sat up and gagged during his execution. He appeared to be choking and his arms seemed to struggle under the sheet, the report said.

In a 2001 execution, again in North Carolina, an inmate appeared to lose consciousness and then began convulsing and opened his eyes, the report said.

The legal assault on lethal injection has been building over the past several years. The Human Rights Watch report, titled "So Long as They Die," highlights admissions from prison officials in several states that no medical professionals were involved in developing lethal injection procedures and that prison personnel are not versed in administering drugs.

For example, when asked in a 2003 court hearing about what considerations went into the development of Louisiana's lethal injection protocol, Annette Viator, former chief counsel for the state penitentiary, said, "The only thing that mattered was that the guy ended up dead."

Dr. Jay Chapman, the former Oklahoma medical examiner who played a key role in developing the original lethal injection procedure, told a Human Rights Watch researcher, "I never knew we would have complete idiots injecting these drugs. Which we seem to have."

Dr. Willie Reed, one of the authors of a veterinary association study on euthanasia, said Michigan State University's veterinary clinic euthanizes animals with "Fatal-Plus," a trade name for sodium pentobarbital, a long-lasting sedative. The dosage is adjusted for the weight of the animal.

Doctors say the drug would probably work effectively in humans, but medical ethics prevent them from proposing a means of execution, even if it is more humane than the process used.