WASHINGTON - Sandra Day O'Connor, the first woman on the Supreme Court and a swing vote on abortion as well as other contentious issues, announced her retirement Friday. A bruising Senate confirmation struggle loomed as President Bush pledged to name a successor quickly. "It has been a great privilege indeed to have served as a member of the court for 24 terms," the 75-year-old justice wrote Bush in a one-paragraph resignation letter. "I will leave it with enormous respect for the integrity of the court and its role under our constitutional structure."