For his part, Mr. Obama has been more willing to address issues like racial disparity and other problems in the criminal justice system since his re-election. He is currently planning to use his clemency powers to release hundreds and perhaps even thousands of drug convicts serving long sentences for less serious infractions.

“I suspect this being his last term, there could be ulterior motives to weaken the death penalty system,” said David B. Muhlhausen, a criminal justice researcher at the conservative Heritage Foundation. “People who believe in the death penalty should be very concerned about this.”

For now, Mr. Obama said his position had not changed.

“The individual who was subject to the death penalty had committed heinous crimes, terrible crimes,” he said of the Oklahoma inmate. “And I’ve said in the past that there are certain circumstances in which a crime is so terrible that the application of the death penalty may be appropriate — mass killings, the killings of children.”

Oklahoma authorities were trying to carry out two executions on Tuesday night when the first one went awry. Clayton D. Lockett, convicted of the murder of a 19-year-old woman whom he shot and buried alive, started writhing in pain as he received the lethal injection drugs, and died later. The second execution was called off.

Mr. Lockett’s ordeal prompted a lawyer for a Missouri death row inmate to ask state corrections officials to videotape her client’s execution scheduled for this month to record any suffering.

Diann Rust-Tierney, executive director of the National Coalition to Abolish the Death Penalty, applauded Mr. Obama’s resolve to investigate concerns about Oklahoma and the use of capital punishment more generally.

“The significant thing is the president as a person who supports the death penalty is expressing these concerns,” she said. “The president is not alone among those who support the death penalty who say this execution crossed the line and has other concerns.”