The amendment in Mississippi would ban virtually all abortions, including those resulting from rape or incest. It would bar some birth control methods, including IUDs and “morning-after pills,” which prevent fertilized eggs from implanting in the uterus. It would also outlaw the destruction of embryos created in laboratories.

The amendment has been endorsed by candidates for governor from both major parties, and it appears likely to pass, said W. Martin Wiseman, director of the John C. Stennis Institute of Government at Mississippi State University. Legal challenges would surely follow, but even if the amendment is ultimately declared unconstitutional, it could disrupt vital care, critics say, and force years of costly court battles.

“This is the most extreme in a field of extreme anti-abortion measures that have been before the states this year,” said Nancy Northup, president of the Center for Reproductive Rights, a legal advocacy group.

Opponents, who were handing out brochures on Saturday to tailgate partiers before the University of Southern Mississippi football game in Hattiesburg, said they hoped to dispel the impression that the amendment simply bars abortions — a popular idea in Mississippi — by warning that it would also limit contraceptives, make doctors afraid to save women with life-threatening pregnancies and possibly hamper in vitro fertility treatments.

The drive for personhood amendments has split the anti-abortion forces nationally. Some groups call it an inspired moral leap, while traditional leaders of the fight, including National Right to Life and the Roman Catholic bishops, have refused to promote it, charging that the tactic is reckless and could backfire, leading to a Supreme Court defeat that would undermine progress in carving away at Roe v. Wade.