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."

Little more than an hour later, Bush praised O'Connor as "a discerning and conscientious judge and a public servant of complete integrity." He said he would recommend a replacement who will "faithfully interpret the Constitution and laws of our country."

O'Connor's decision so closely held that a son did not know in advance marked the first retirement in 11 years on an aging court. It came as a modest surprise, particularly since Chief Justice William Rehnquist has been the subject of retirement rumors for months. Rehnquist, 80 and ailing with thyroid cancer, has offered no hint as to his future plans.

O'Connor's decision capped a pioneer's career. President Reagan broke nearly 200 years of tradition when he tapped her a top-ranked graduate of Stanford law school for the high court.

Over time, she evolved into a moderate conservative, but more importantly, a majority maker.

She voted with a 5-4 majority, for example, on the case that effectively awarded the disputed 2000 presidential election to Bush. She was on the winning side again when the court upheld the right of women to have an abortion if their health were in danger.

She expressed her views pungently at times. Last week, in a dissent in a 5-4 ruling that let local governments take personal property to build malls and other businesses, she wrote that the majority had unwisely handed more power to the powerful.