Dr. Kenneth C. Edelin, a Boston physician whose 1975 manslaughter conviction for performing a legal abortion was overturned on appeal in a landmark test of medical, legal, religious and political questions surrounding abortion in America, died on Monday in Sarasota, Fla. He was 74.

The cause was cancer, his family said.

Two years after the Supreme Court's Roe v. Wade decision legalized abortion in 1973, Dr. Edelin, a 35-year-old resident in obstetrics and gynecology at Boston City Hospital, became the focus of a roiling national debate over crucial issues that had been left unresolved by the justices: When does life begin? Does an aborted fetus have rights? And what are a doctor's often contradictory duties to the fetus and its mother?

Dr. Edelin (pronounced EE-da-lin) was charged with causing the death of the fetus of an unwed 17-year-old during an elective abortion in her sixth month of pregnancy. In a six-week trial in Boston that explored uncharted legal ground and made headlines across the country, Dr. Edelin, who was black, was vilified as a baby-killer and defended as a victim of racial and religious prejudice being tried for an action that had never been defined as a crime: killing a fetus that may or may not have been a "person," and whose rights had never been specified by law.

The abortion, which took place in 1973, began as a routine procedure: the injection of a saline solution that usually causes uterine contractions and the expulsion of the fetus. But several tries were unsuccessful, and Dr. Edelin completed the abortion by a surgical procedure known as a hysterotomy — making a small incision in the uterus, like a cesarean section, and detaching the fetus from the placental wall by hand.

Prosecutors did not contest the legality of the abortion — Roe v. Wade had struck down anti-abortion laws in most states, including Massachusetts — but argued that Dr. Edelin, after ending the pregnancy, had deprived "a baby boy" of life-sustaining oxygen while it was still in the womb "being born." A photo of the dead fetus preserved in formaldehyde was shown to the jurors, and some said they were "shaken" by it.

The defense called the photo inflammatory and objected repeatedly to the prosecution's use of "fetus" and "baby" as interchangeable terms in a case it said was being politicized. Medical experts testified for the defense that the fetus, estimated to be 24 weeks old, was not viable enough to have survived outside the womb. Dr. Edelin's lawyers contended that no "person" had even existed, let alone died.

But the all-white 12-member jury, which included nine men and 10 Roman Catholics, convicted Dr. Edelin of manslaughter. Some jurors said later that the photo of the dead fetus, whose face, they said, looked distorted as if in pain, had been decisive in their decision to vote guilty. An alternate juror also said after the verdict that jurors had made racial slurs against Dr. Edelin "more than once" before closing arguments.

The presiding judge, who had instructed the jury that it could convict only if it believed that the fetus was a viable person and that the doctor had acted recklessly, sentenced Dr. Edelin to one year of probation, although he could have imposed a maximum of 20 years in prison. Dr. Edelin kept his medical license and continued to practice at Boston City Hospital.

The verdict was hailed as a victory by anti-abortion groups and the Catholic hierarchy, which had long contended that life was sacred and began at conception. But it shocked and dismayed advocates of women's rights, who called the case a precedent that could make doctors wary of performing abortions in the second trimester.

Dr. Edelin called the prosecution a "witch hunt" in a city where a huge Catholic population believed that fetuses were human beings with the rights of citizens, and that abortions were sacrilegious. The chief prosecutor, Assistant District Attorney Newman A. Flanagan, was himself a Catholic who hoped to run for Suffolk County district attorney, and was widely admired for pursuing a case that might tighten restrictions and intimidate doctors who performed abortions.

Dr. Edelin appealed the verdict, and in 1976 the state's highest judicial body, the Massachusetts Supreme Judicial Court, unanimously overturned the conviction and formally acquitted him.