It's one of the most promising medical frontiers in the search for cures to human diseases that kill and cripple.

It's also a minefield of moral and ethical issues that's divided public, political, scientific and religious opinion.

John Gearhart, the director of research at the Johns Hopkins School of Medicine in Baltimore, brought the case for embryonic stem cell research to Las Vegas on Monday.

Gearhart has spent the past 20 years researching the causes of mental retardation and birth defects, which led him to where he is now: research into the use and culturing of human stem cells that may hold the key to regenerating diseased tissues in the body.

"We're a long way from putting any of these things into human beings," Gearhart told an audience of about 400 people gathered at UNLV's student union, after flashing through a slide show that showed amazing improvements in defective pig hearts and crippled rats that were treated with stem cells during experiments.

Gearhart acknowledged that the problem is in formulating the potential cure: The stem cells are derived from microscopic embryos, a source that has drawn opposition from people and organizations dedicated to the idea that human life begins at conception.

"A major issue is the moral value you ascribe to these structures," Gearhart said, standing in front of a projection illustrating the microscopic structures from which stem cells are derived. "What is an embryo? What is not an embryo?"

Kathleen Miller, director of Nevadans for Life, a nonprofit group that espouses pro-life issues, said she was not opposed to stem cell research as long as those stem cells don't come from embryos.

Much work is being done in the area of adult stem cells and stem cells derived from umbilical blood and placentas.

"I'm absolutely in favor of ethical stem cell research," said Miller, who was invited to take part in a public discussion that followed Gearhart's lecture.

But to Miller, embryonic stem cell research could never be ethical.

The problem presented by that school of thought was touched on by Gearhart, who pointed out that only embryonic stem cells have the potential to replace any of the 220-plus cell types in the human body.

There are also other limitations on nonembryonic stem cells, Gearhart said.

There are no available adult stem cell sources for human motor neurons, which connect the brain with the skeletal muscles, and those are the kind of cells needed for research into a cure for amyotrophic lateral sclerosis, or Lou Gehrig's disease.

Other nations are outpacing the United States in stem cell research, largely because of the political obstacles that the federal government and some state governments have set up against embryonic stem cell research.

Public money for stem cell research in the United States is only a fraction of the money being spent in other nations, Gearhart said.

Audience members reflected the rift that Gearhart highlighted. After his speech, Rancho High School junior Alodie Haines left unconvinced.

"Personally, I don't believe in embryonic stem cell research," said Haines, who is enrolled in Rancho's medical academy and plans to become a plastic surgeon.

UNLV criminal justice major Amber Lasby was uncertain.

"I just don't know," Lasby said. "I feel that embryos are babies. But if it could help someone in my family, I don't know. I might agree."