When Supreme Court justice Potter Stewart announced his retirement in 1981, President Reagan summoned a former Republican activist and lawmaker, a judge sitting on the Arizona Court of Appeals, to the Oval Office. Sandra Day O'Connor was a wife, married for almost 30 years at that point to a law school classmate; a mother, whose three boys were nearly grown; and a daughter of the West, whose rancher daddy taught her to brand cattle and brandish a .22 by the time she was 8.

Reagan said later she charmed him immediately with her passion for horses, which he shared. They chatted about judicial issues; he never mentioned the Supreme Court opening.

She said later she "got on the airplane and sat down and took a big breath and said, 'My, that was an interesting time to go to Washington. But thank goodness I don't have to do that job.' "

O'Connor, 75, yesterday announced she is giving up "that job," which she held for nearly a quarter-century. For much of that time, she has been described as the most influential woman in America, a designation that always stuck in her craw. The way she was raised, and the way she has lived, is simply to work hard and attentively in all the realms of her life, from the law to the Arizona Senate to court trials, from the Junior League to her golf game, from her friendships to her 1988 battle with breast cancer.

"All her life, whatever she did, whether it was important, or unimportant, or semi-important, or very important, she just would do it to perfection," her younger brother, H. Alan Day, told The Post years ago. "If you said, 'The job is to wash dishes well,' she would do it better than anyone else."

The very nature of her vaunted position has allowed her to blend and balance all these realms with a grace and dignity many powerful women never achieve. Outside the publicity glare that descends on first ladies and female politicians, O'Connor in Washington created quite a modern model for any women who hope to fashion lives both professionally and personally full. She is her own mix of frontier woman and distinguished jurist, able both to mug in a cowboy hat and to cast the crucial swing vote in more than a dozen 5-4 decisions.

Friends and family members have said she is a down-to-earth woman, generous and funny, given to throwing birthday celebrations for her clerks and sending thank-you notes seemingly written as soon as she arrived home.

But she is also reserved and private; her own son told the Associated Press that yesterday's resignation caught him by surprise. In her letter to President Bush, the justice made no mention of why she was ending her lifetime appointment. Supreme Court spokeswoman Kathy Arberg said O'Connor said she "needs to spend more time with her husband," John, 75. The justice has told close friends that he is suffering from Alzheimer's. None of the couple's three sons and six grandchildren lives in the area.

Her husband has been a full partner in her life from their days at Stanford Law School, where they were editors on the law review. Sandra Day graduated third in her class (first in the class was William Rehnquist, now the chief justice). The two of them dated, "a few movies and one thing or another," as O'Connor explained it, but once she accepted a date from John O'Connor, they had dates the next 39 nights in a row, "until he decided he needed to get some rest," she said.

When she brought O'Connor back to the 198,000-acre ranch straddling Arizona and New Mexico, her father tormented him by taking a piece of baling wire, skewering the testicles of the bull he had just castrated and grilling them in the branding fire. Then he held out the delicacy, standard cocktail-hour fare on the Day ranch, and said, " 'Here, John, try these.' " O'Connor recalled. "And poor John, he had to take one and gulp, 'Very good, Mr. Day.' " With that test passed, the couple wed as soon as she graduated law school. She was 22.

None of the law firms in California would hire her as a lawyer, although she did get an offer to be a secretary, "depending on my typing," she likes to recall, and not with total amusement, even all these years later.

She took a job as a deputy county attorney. After her husband's military tour of duty in Germany, he got a well-paying corporate job in Phoenix and she hung out a shingle with another attorney. When her second child was born in 1960, she decided to stay at home. She threw herself into volunteer work, becoming president of the Phoenix Junior League, and kept her hand in the law with the occasional appointment as trustee in a bankruptcy case and juvenile court referee.

During the '60s, she was an assistant attorney general in Arizona, then served out the term of a state senator who stepped down. She won two elections on her own, and became the first woman in the country to be a Senate majority leader in 1973. A year later she moved to the bench and was appointed to the state's appeals court in 1979.

She had not fixed herself to a particular life course. "I don't think it would be fair to say that, for Sandra, drive was one of those things that meant she must get to a specific goal," Hattie Babbitt, an attorney, told The Post in 1986. She urged her husband, Arizona Gov. Bruce Babbitt, to appoint O'Connor to the state court. "The kind of drive she has is she's very smart, and very organized, and she would always want to be very good at what she does. You can do that and not be in the right place at the right time. But she did and she was."

It was John O'Connor to whom she turned when President Reagan called and asked if she would accept his nomination to the Supreme Court. She hesitated, not sure what to do. A move for her meant career upheaval for him. "You cannot say no to the president," he told her.

But the woman whose style is to make decisions and resolutely never look back arrived in the nation's capital scared to death. "I felt intimidated by Washington and everything there," she told George Vradenburg, chairman of the Phillips Collection. She loved her Arizona, and the way the expanse of limitless sky and land kept a person humble. Frequently, she evoked author Wallace Stegner to describe her feelings for the West: "There is something about exposure to that big country that not only tells an individual how small he is, but steadily tells him who he is."

She and her husband eventually settled in Chevy Chase and joined the exclusive Chevy Chase Club. She took up golf with her usual perseverance bordering on obsession, taking lessons with a pro and hitting buckets of balls every Saturday for four years before she ever set foot on the course. Her first outing, she broke 90.

Over the years, O'Connor and her husband maintained a social schedule that could seem almost frenzied. They are sought-after guests at A-list parties, popping up often at the Kennedy Center, the National Gallery of Art and embassies around town. "She and John were often the very first on the dance floor," said Walter Cutler, president of Meridian International Center. "They just love to dance. They had a unique dance step -- I wouldn't call it a Charleston, but it has that same festive air."

In 1985, O'Connor was seated at the head table at the Washington Press Club's annual dinner, where Redskins star John Riggins drunkenly told her, "Loosen up, Sandy baby. You're too tight!" Then he passed out on the floor. An embarrassed Riggins sent apologies and roses the next day. Seven years later, Riggins appeared in a play at a suburban Washington theater, and O'Connor presented him with a dozen roses during the curtain call.

When asked for a comment yesterday about the infamous incident, Riggins, with his characteristic politesse, hung up on a reporter.

O'Connor, on the other hand, is well known as a great dinner partner: curious, lively, engaged, with a dry sense of humor and knack for telling stories.

Her ranch upbringing had isolation, deprivation and years of financial distress, but her parents were highly cultivated people. They subscribed to the Wall Street Journal, the Los Angeles Times, the New Yorker, Vogue and Time. Her mother was a college graduate who ordered her clothes from Neiman Marcus and Saks; when she drove her daughter into town, 25 miles away, to get the mail, the residents would crowd around just to see what Ada Mae Day was wearing.

Her daughter has taken full advantage of what can be fascinating and stimulating in the capital city.

"I've watched her in social situations, and what you find is that there is no limit to her interests," said philanthropist Catherine Reynolds. "She is interested in everything. She just embraces life and all it curiosities." Reynolds seated country singer Dwight Yoakam next to O'Connor at a dinner in March. "He must have thanked me a dozen times. He said it was the most interesting night of his life. He just enjoyed her tremendously."

Two years ago, Reynolds and her husband, Wayne, brought more than 200 graduate students to Washington to meet with politicians, scientists, historians, businessmen and artists. They asked O'Connor to speak to the group, and they were all invited to the Supreme Court chambers, where they heard O'Connor and Ruth Bader Ginsburg talk about the court, the Constitution and the decision that gave the 2000 election to George W. Bush.

"She is so special," said Reynolds. "She is a great inspiration for young people from all around the world, but especially young women. She's very forthcoming in talking about her experiences and her struggles. . . . When she talks to you, you get that sense of authenticity, how real she is. You feel a connection with her."

O'Connor seemed especially solicitous of female clerks with children. University of Florida law professor Barbara Bennett Woodhouse, who was a 40-year-old mom when she clerked 20 years ago, recalls how the justice insisted that Woodhouse fly to Connecticut to see her 11th-grade daughter perform Gilbert & Sullivan.

"She said, 'This is a must-attend event.' She picked up the phone, called her travel agent and told me about the flights," said Woodhouse. "She had a very strong appreciation for the importance of our families."

Twenty-three years ago, she summoned yoga and aerobics instructors to hold 8 a.m. classes for women working in the Supreme Court; they're still going strong, and O'Connor joins in. "She was a big believer in the well-rounded life," said another former clerk, Marci Hamilton, now a Cardozo School of Law professor. "She is the opposite of the 24-7 law partner. . . . A very human person. . . . She never let anyone believe that law was the beginning and end of your life."

As hard on her clerks as she was on herself, she counterbalanced her demands for excellence and long hours with warm gestures: they recall how she'd swoop into the office and announce an impromptu afternoon jaunt to see the cherry blossoms or, on one occasion, a new Degas exhibit at the National Gallery. She also set up weekend field trips: horseback riding in Rock Creek Park, rafting in West Virginia, a visit to Harpers Ferry.

She even cooked lunch for Saturday sessions at which she and her clerks discussed upcoming oral arguments. "That was my introduction to green chili casserole," recalled Phoenix lawyer Scott Bale, an O'Connor clerk in 1984-85. "It left me with a long-term affection for green chili."

As she has nurtured relationships on the court, keeping her ties with Rehnquist and playing bridge with justices Anthony Kennedy and Stephen Breyer, she has built "deep and lasting friendships," said Lynda Webster. She and her husband, former FBI and CIA director William Webster, are close friends of the O'Connors and share a passion for fly-fishing, tennis and golf. "She's a go-getter," said Webster. "She's game for anything. She really has an incredible zest for life."

The couple told some friends they were giving up their Chevy Chase home and purchasing an apartment on New Mexico Avenue.

The Websters and the O'Connors had dinner together last week, but Webster said neither she nor any other of O'Connor's friends had a hint of the pending resignation. "None of us knew, but then again, we would never ask."

Staff writer Richard Leiby and researcher Karl Evanzz contributed to this report.

Justice Sandra Day O'Connor's Western heritage continued to inform her life long after she left Arizona for Washington. Sandra Day O'Connor and her husband, John, at the Meridian Ball in 2002. "They were often the very first on the dance floor," says a friend.O'Connor dressed for golf in 1979. Intense about succeeding on the links, she broke 90 her first time out at Chevy Chase Club.Elizabeth Dole with the O'Connors in 1981, after her Senate confirmation hearings concluded.O'Connor's affection for horses, which dates to her childhood, helped her charm President Ronald Reagan. At right, she receives an honorary degree from Georgetown's law school in 1986.