Helene E. Weinstein owes her Assembly seat, in part, to capital punishment.

In 1978, her father toppled the Assembly speaker, Stanley Steingut, a death penalty opponent, from his Brooklyn district, in an upset that sent shock waves through state politics. Two years later, Ms. Weinstein herself was elected to the seat, and consistently voted in favor of the death penalty.

But in a shift that reflects the changing passions on capital punishment among the public and its elected officials, Ms. Weinstein these days harbors serious doubts about the death penalty. And now, having risen to become chairwoman of the Judiciary Committee, she is poised to doom New York State's on-again-off-again death penalty law.

"It was an evolutionary process," Ms. Weinstein said the other day, explaining her shift. "But clearly the advent of DNA evidence and the dramatic number of individuals who have been exonerated and freed from death row in states around the country was something that was building in my mind."

Such are the paradoxes of politics - of politics as practiced in Brooklyn, anyway - that Ms. Weinstein's father, Murray, not only still supports the death penalty, but now admits that his support for capital punishment began only during the campaign against Mr. Steingut.

"I switched in 1978," he recalled. "Steingut was against it and I needed a point of distinction."

Mr. Weinstein also expressed some doubt about the depth of his daughter's support for capital punishment. "I always thought she was uncomfortable in her position," he said, "but obviously she supported it all along to be consistent."

Ms. Weinstein, who was 25 when she first ran for the Assembly, said she did not precisely recall when she became an advocate of capital punishment. "I assume when I first ran for office," she said. "I'm not sure that I had focused on it before. I felt comfortable voting for the death penalty. That was my position."

Other issues also helped to cost Mr. Steingut his seat, particularly the view among many voters that he had lost touch with his district. But rising violent crime, a number of sensational murders and Gov. Hugh L. Carey's veto of legislation that spring to restore capital punishment all resonated loudly in the primary and general election campaigns for state offices that year. Mr. Steingut allowed the death penalty bill to get to the floor of the Assembly, but voted against it.

Mr. Steingut, who was first elected to the Assembly in 1952, the year Ms. Weinstein was born, was singled out on two levels in 1978. Theodore Silverman, a local city councilman, wanted his wife to be Mr. Steingut's co-district leader but was rebuffed and vowed revenge. Andrew Stein, then the Manhattan borough president, was dismayed that Mr. Steingut had not been legally implicated by his association with figures in a nursing home scandal, so, he explained at the time, "subjectively and politically I made up my mind to destroy him."

Ms. Weinstein was the chosen vehicle to defeat the speaker, but her residency was challenged, a maneuver that inadvertently heightened resentment against Mr. Steingut, who, with his father, had represented the district for more than a half century. She was forced off the ballot, and her father, Murray, a 50-year-old lawyer, replaced her. Less than two weeks later, he upset Mr. Steingut in the Democratic primary. Mr. Weinstein reluctantly relinquished the seat to his daughter two years later.

"She was entitled to it," he recalled. "She really ran for it."

After Ms. Weinstein came to Albany, Gov. Mario M. Cuomo, like Mr. Carey before him, vigorously opposed the death penalty. He was defeated in 1994 by George E. Pataki, a Republican, who 10 years ago next month signed a law reimposing capital punishment for first-degree murder. Last June, the State Court of Appeals ruled that a central provision of the law was unconstitutional, effectively suspending the death penalty in the state.

Governor Pataki proposed a quick fix, and the Republican-controlled Senate concurred last summer. But after holding five joint hearings, members of three committees in the Democratic-run Assembly, including Ms. Weinstein's, doubt whether any death penalty bill can pass constitutional muster or whether, politically, one seems as vital as it did a decade or more ago.

Ms. Weinstein attributes those doubts to several factors: crime has sharply declined; the law now provides for the option of life imprisonment without parole; evidence has mounted that black and Hispanic inmates are disproportionately executed; and the number of death-row inmates who have been exonerated nationwide has given even hardened capital punishment supporters pause.

"I saw the play 'The Exonerated,' " Ms. Weinstein said. "It had tremendous impact on me."

Since the early 1990's, as crime plummeted, proponents of capital punishment have maintained that the death penalty has, at least, been a deterrent.

"I believed when I voted for it that there was a deterrent effect," Ms. Weinstein said. "I am pretty convinced now that there isn't. No one ever thinks he's getting caught, and the likelihood that you're going to get caught, convicted and receive the death penalty is so remote."

Ms. Weinstein recalled testimony at the Assembly hearings, which ended earlier this month, from a district attorney who supported capital punishment in principle but opposed reinstatement of the statute because death penalty cases cost taxpayers too much to prosecute and to defend and because no version could be legally foolproof.

She also recalled testimony from another law enforcement official who said that if he were convicted he would rather be executed than be sentenced to life without parole, and the testimony of a judge who warned that a higher standard of proof than beyond a reasonable doubt must be required. And she said she had heard from witnesses who said the death penalty was more likely to be sought when the victim was white and the defendant was black.

"The chance of unequal justice and the part that racism plays I found very disturbing," Ms. Weinstein said.

Moreover, she added, hiring public defenders and other costs mean that about $170 million has already been spent on a death penalty that has not resulted in a single execution.

"We could have spent more on other criminal justice and social programs," she said.

After reviewing the testimony, Ms. Weinstein said the committee heads would report to the Assembly.

"I think it was impossible for anyone to sit through the testimony and not come away with the conclusion that you cannot draft a death penalty law that does not have the possibility of convicting someone who is innocent," she said. "It seems clear to me that from all of what we've heard the chance of convicting an innocent individual remains a possibility, and there's no way to rectify that. People are seeing that the justice system is not infallible."

Reminded of her position a decade and longer ago, Ms. Weinstein was asked how she could be sure she was right this time.

"I'm not sure there's anything as dramatic or as important as the death penalty in terms of my vote," she replied. "I have certainly looked at legislative proposals I supported or opposed and become convinced there's room for a change of position. Times and evidence have changed. That is the wonderful thing about a mind: You can change when you hear evidence and make an intelligent choice."