It's the thorny question at the center of the decades-old national abortion debate, and a sticking point in proposed state laws that would add extra penalties to crimes against pregnant women.

If lawmakers approve a bill now in play in the South Carolina Legislature, fetuses will receive rights to due process from the moment of fertilization -- weeks before a plus sign or a colored line on a home-pregnancy test can confirm the news.

The bill's sponsors say it's not intended to address abortion rights -- for now. Instead, they say they're seeking to protect babies injured along with their mothers through accidents and violence, when doctors often must make split-second calls about how to proceed with treatment without harming the fetus.

The language in the bill, however, could land it in the courts because it appears to be at odds with the rights guaranteed to women by Roe v. Wade, the U.S. Supreme Court decision that legalized abortion across the nation in 1973.Reproductive rights advocates also worry that such a law could interfere with other women's health concerns, such as birth control and fertility treatments.

"It's real clear what they're doing," said Walter Klausmeier, president and CEO of Planned Parenthood Health Systems Inc., which runs eight health centers in the Carolinas and West Virginia. "It's just one more way to chip away at the constitutional right of a woman's right to chose."

Indeed, sponsors of the law say part of their plan is to lay the groundwork to restrict or outlaw abortions in South Carolina if the Supreme Court reverses its landmark decision on abortion rights. At that time, states would be allowed to decide whether to allow the procedure, and under what circumstances.

"If Roe v. Wade is overturned, this bill would become the law of South Carolina," said Rep. John Graham Altman, R-Charleston, who sponsored the House bill along with 45 others. "I don't think there's an appetite in the South Carolina Legislature to criminalize every person who has an abortion, but I would expect there to be some limits."

The effort is among a number of similar laws recently enacted across the nation, as states begin preparing for what some legal observers predict is the inevitable overturning of Roe. The South Dakota Legislature, for instance, recently passed a "trigger law" that would ban all abortions except when necessary to save a mother's life if Roe falls.

Other states have recently voted to strengthen parental notification laws, criminalize fetal injuries during assaults of pregnant women and mandate fetal anesthesia during abortions.

The South Carolina bill, however, calls for something new, something more contentious: a sweeping change to the definition of when personhood, and its inherent rights to life and liberty, begins.

"I've never heard of anything like this before," said Judy Waxman, vice president for health and reproductive rights at the National Women's Law Center in Washington, D.C. "There are serious constitutional questions being raised here."

Emboldened by President Bush's opposition to abortion and the infirmities of some aged justices who are expected to step aside before the end of Bush's second term, pro-life groups both in South Carolina and around the country are hopeful Roe v. Wade soon will be dismantled. Bush hasn't had the chance to make a Supreme Court appointment yet.

In the meantime, pro-lifers applaud any state legislation that furthers discussion about the value of "preborn" life.

"Any bill that would work toward preserving life is going to be a good thing," said Nancy Mixson, director of Alpha Crisis Pregnancy Center in Summerville. "I'm sure there's going to be a lot of complexities with this, but the law is established to protect the people, and of course this little person in the womb is a people."

Sponsors of the Right to Life Act, expected to come up for a floor vote in the House this week, say they're prepared for court challenges if the bill passes.

"The courts are the liberals' playpen," Altman said. "I expect the liberals will bring some sort of action, some time, in their zeal to kill not-yet-born babies."

At this stage, there are few clues about how the law would be put into practice, such as how people would be appointed to represent a fetus' interests, or how the needs of the mother would be weighed against those of the fetus.

"How could someone know what the zygote's wishes would be?" Waxman said. "This is so vague, anybody can claim almost anything under it."

The half-page bill merely states that a fetus is entitled to due process and equal rights beginning at fertilization. Waxman worries that overbroad fetal rights legislation will lead to limiting other aspects of reproductive liberties. Eventually, a woman's right to birth control pills, or a couple's ownership of frozen embryos stored at fertility clinics could all be called into question, she said.

Altman said the statute wouldn't seek to govern what happens in such clinics, since the embryos aren't yet being carried by a woman. "That would not be the intent at all," he said. "Those frozen embryos are in the process of creating life, not ending it."

But what about when couples decide they don't want any more children, or can't endure more expensive and often painful fertility treatments? Would throwing the leftover embryos away leave them open to prosecution?

The answers are unclear.

The effects of the bill could also spill into other areas of the law, said Eldon Wedlock, a professor of constitutional law and criminal procedure at the University of South Carolina's law school. A greedy daughter, for instance, could attempt to lay additional claim to a parent's estate on behalf of her fetus.

Doctors, meanwhile, are puzzled about the true intent of the law, since the mandates of basic biology lay out their tasks for them in an emergency situation involving a pregnant woman.

Rare would be the times doctors would truly be forced to choose between the life of a mother or her baby, said Dr. Doug Norcross, medical director for trauma services at the Medical University of South Carolina.

"We save mom," he said. "That's the way you save babies."