“I’m a conservative guy — I’ve been a Republican my whole life,” he said in an interview. “A lot of my conservative colleagues have come to the conclusion that we’re there to root out inefficient government programs. Some people see this as a pro-life issue. Other people see it as a good-government issue. But the support that this bill is getting from conservative members is evidence that you can get justice through eliminating the death penalty, and you can get efficient government through eliminating the death penalty.”

But other Republicans, dismayed over what they see as a deviation from the party’s core beliefs, have vowed to fight the measure. Senator Bill Kintner, who opposes repeal, said a filibuster had been discussed to try to stop it.

Those lawmakers in his party who favor the bill, Mr. Kintner said, have lost their way. “Conservatives have always been the bedrock of law and order,” he said in an interview in his office in the Capitol. “We want to make sure our streets are safe.”

Yet even some lawmakers who ultimately voted against the bill on Friday said they had lost sleep trying to decide. “I have struggled with this issue,” Senator Dave Bloomfield said. “At the end of the day, I will be voting to keep the death penalty on our books as an alternative to the most heinous crimes.”