WASHINGTON — The Supreme Court agreed Monday to consider a major rollback of abortion rights, saying it will decide whether states can ban abortions before a fetus can survive outside the womb.The court’s order sets up a showdown over abortion, probably in the fall, with a more conservative court seemingly ready to dramatically alter nearly 50 years of rulings on abortion rights.The court first announced a woman’s constitutional right to an abortion in the 1973 Roe v. Wade decision and reaffirmed it 19 years later.The case …