The Supreme Court's decision to take on Nebraska's law banning so-called partial- birth abortions virtually guarantees that the rending issue of abortion will dominate the presidential campaign to a degree likely to help Democrats more than Republicans.

The decision also puts in peril women's rights to abortion first articulated in Roe v. Wade in 1973 and reasserted in the court's 1992 decision Planned Parenthood v. Casey. That decision held that abortion was constitutionally protected and a part of a woman's fundamental right to privacy. But it also allowed states to promote childbirth over abortion by requiring waiting periods and other elements to dissuade women from that course of action, as long as these did not constitute an undue burden on the woman. Both decisions held that states can ban only abortions performed after the fetus is viable, and then only if these bans provide exceptions to protect the woman's life and health.

In the past few years, abortion opponents, despairing of judicial overthrow of fundamental abortion rights, have tried to get bans on the procedure through a series of clever, backdoor maneuvers in state legislatures. Their ostensible target has been a procedure known medically as dilation and extraction, or D&X. The state and federal bills advanced by abortion opponents use strikingly familiar language, defining this type of abortion as "an abortion in which a person partially vaginally delivers a living child, causes the death of the partially delivered child with the intent to kill the child, and then completes the delivery of the child."

These laws state that a child's life begins at the moment of conception. The procedure is rarely done to terminate a pregnancy that has lasted only 16 weeks, but this description fits the more common forms of abortion that are performed at the end of the second trimester. These laws generally don't provide exceptions to protect a woman's health or for pregnancies resulting from incest or rape, and they provide harsh criminal penalties for doctors performing the procedures. So far, 30 states have passed a version of this law.

The majority of the laws have been promptly struck down as unconstitutional. The Center for Reproductive Law and Policy has challenged these laws in 14 states, including Nebraska, whose law would include most common abortions. On Dec. 15, the center petitioned the Supreme Court to affirm a lower court's decision that Nebraska's law was unconstitutional. On Friday, the court agreed to take the case, marking the first time it has taken up the contentious issue since 1992.

What brought this about were two very different findings on the constitutionality of these laws, handed down within a month of each other last fall, the first by the 8th U.S. Circuit Court of Appeals and the second by the 7th Circuit.

The 8th Circuit struck down Nebraska's law, finding it would ban several common abortion procedures and thus impose an undue burden on a woman's right to abortion. The court struck down Arkansas' law and Iowa's on similar grounds.

On Oct. 26, the 7th Circuit Court, in one of the most tortured arguments put to paper, upheld as constitutional bans in Illinois and Wisconsin. Supreme Court Justice John Paul Stevens, the circuit justice for the 7th Circuit, granted a stay of that circuit's decision, pending a decision by the full court to review the cases.

The announcement that the court would review these cases was greeted with cautious optimism by Janet Benshoof, president of the Center for Reproductive Law and Policy. Given the split between the two circuits, she said, "a high court remedy is needed to clarify the extent to which states can stop abortions." She underscored important points about what is at stake: These cases are not about abortions late in pregnancy, she said. The 8th Circuit opinion under review is strictly about the law's impact on pre-viability abortions. The Nebraska ban that has been upheld outlaws the most common and safe abortion procedures in use. What's at stake is whether women will continue to be able to make private medical decisions without interference from legislatures, religious groups and busybodies, or whether states can outlaw abortion by banning the most common procedures.

The two Democratic presidential candidates are pro-choice. The Republican presidential candidates range from making an antiabortion platform a campaign centerpiece to merely declaring themselves to be against abortion.

The gruesome descriptions of the D&X procedure have prompted popular support for these laws. But gruesome should not be a legal standard for outlawing medical procedures: A mastectomy, for example, is to my mind gruesome. Doctors have testified that in many cases, D&X is the safest procedure for protecting a woman against infection and dangerous fetal remnants. Most Americans have been on record for years as saying they believe the decision to end a pregnancy should be made by a woman and her doctor. This is the heart of abortion rights. It is a central tenet of a woman's right to manage her own life.

The next president will probably have a chance to name a chief justice and one or two other justices and fill many vacancies in the lower federal courts, which means he will have a lasting impact on how the federal judiciary treats abortions.

The Supreme Court will hear arguments on these cases in April, with a ruling expected in June, just as the presidential campaign goes into its final months. When abortion rights are threatened, women voters, particularly younger ones, get galvanized into political action. It will become very clear in the months ahead that abortion rights are still under siege and that it is the Democrats who are guarding the ramparts.