GENEVA (AP) -- Swiss voters overwhelmingly approved a law allowing stem cell research Sunday, rejecting a hard-line campaign that compared researchers to the Nazis' "angel of death," Dr. Josef Mengele.

Some 66.4 percent of those polled - or 1.1 million voters - approved the law passed by the government last December. The law will take effect in March.

Opponents had called the referendum to try to overturn the legislation, even though it sets stricter limitations on research than exist elsewhere in Europe. The Swiss bill only allows the use of embryonic stem cells left over from in-vitro fertilization.

Embryonic stem cells form in the days after fertilization and can turn into any tissue of the body. Many researchers believe stem cells harvested from embryos could be used to regenerate nerve tissue or cure diseases, including Alzheimer's. But extracting stem cells from an embryo kills the embryo, which opponents say is tantamount to taking a life.

In the United States, President Bush has approved federal funding of embryonic stem cell research for only the 78 stem cell lines in existence on Aug. 9, 2001. At last count, less than two dozen of those lines are still available.

The government said the law will permit Switzerland - which has major pharmaceutical and biotechnology companies - to take part in vital research.

The opposition alliance, which included Roman Catholics and Protestants as well as left-wing and green groups, said the defeat was a setback for scientific ethics.

"In a few years, we will be voting on therapeutic cloning," said Pascale Steck of the referendum committee.

One opponent organization, Familiaplus, distributed a petition titled "No to Dr. Nazi Mengele," a reference to the doctor who conducted infamous human experiments at the Auschwitz death camp during World War II.

The government said the law strictly prohibits human cloning or the creation of embryos for stem-cell research and stressed the restrictions on the research, which include a requirement for the written consent of the parents, the approval of an ethics committee and the Swiss Health Ministry for each research project.

European nations that permit stem cell research include Sweden, Finland, Greece and the Netherlands. Britain allows the creation of human embryos for stem cell procurement.