In interviews, Justice Sandra Day O'Connor routinely dismissed the notion that she was a crucial "swing vote," the justice who could sway the nation's highest court one way or the other. Every vote on the court is equal, she would say, no one counting more than any other.

She could afford to scoff. But the litigants and their lawyers could not.

In fact, they crafted their arguments carefully with her in mind, scouring all her writings to make sure they addressed any specific concerns she might have, believing that if they won her, they were considerably more likely to win the case.

It wasn't because she was intrinsically more important than the others. Rather, as she once said, she was "open to persuasion" while some others were not.

Sandra Day O'Connor's influence on the nation's highest court was so great that some academics had come to call it not the "Rehnquist Court," after the Chief Justice, but the "O'Connor Court."

She arrived on an ideologically divided high court during a period of unprecedented challenge to established law on issues such as abortion, affirmative action, church-state relations and criminal justice.

She put her stamp on each of these fields, not by adopting an agenda, but by avoiding one.

She deployed her strategic role to moderate the extremes, ultimately standing in the way of most of the conservative movement to turn the court around.

She helped modify the right to abortion but blocked the efforts of conservative colleagues to overturn it.

She rejected challenges to the use of affirmative action in higher education, instead endorsing its use in narrow circumstances in the interest of "effective participation by members of all racial and ethnic groups in the civic life of our nation. . . . "

In what may be her most memorable opinion, she was willing to grant considerable deference to the Bush administration's anti-terrorist detention policies but drew a firm line at the policy of detaining individuals without independent review.

"It is during our most challenging and uncertain moments that our Nation's commitment to due process is most severely tested," she wrote last year for the court in the Iraq-war era case of Hamdi v. Rumsfeld. "And it is in those times that we must preserve our commitment at home to the principles for which we fight abroad. . . . We have long since made clear that a state of war is not a blank check for the President when it comes to the rights of the Nation's citizens."

Her opinions were by no means her main claim to distinction.

As Thurgood Marshall was the first black jurist on the court, so she was the first woman.

For women lawyers, she symbolized a long struggle first for admission to the profession of law and then for access to the upper reaches. She regaled audiences with her own story: how she graduated third in her class at Stanford Law School but could get in the door of only one major law firm, where she was then duly informed it did not hire women lawyers and offered a secretarial position.

" 'Miss Day,' " she recalled being asked, " 'how do you type? We don't hire women and I don't see the day when we will.' "

Thirty years later, Supreme Court Justice O'Connor found herself addressing the members of that firm, Gibson, Dunn, and she taunted them good naturedly. "You rejected me," she reminded them. "So I had to settle for just a small firm -- a firm of nine."

O'Connor's unique status as the first female on the court, combined with a gregarious public presence unusual for the government's most monastic branch, made her unquestionably the best-known justice in modern times, greeted by strangers in airports and on the streets and always named on pollsters' lists of America's most powerful and most respected women.

Sandra Day was born on August 26, 1930 in El Paso, Texas. She was raised virtually as the only child of Harry A. and Ada Mae Day on a vast ranch, the Lazy B, along the Arizona-New Mexico border. Her sister, Ann, and her brother, Alan, wouldn't come along until eight and 10 years after her.

Harry Day was the son of a Vermont Yankee who had come west in search of adventure and the money to be had in cattle ranching; Ada Mae was the cultured daughter of an El Paso merchant and banker. While Ada Mae was one of the rare women college graduates of her day, Harry-who had planned to go to Stanford-was called back to the family ranch in the late 1920s to untangle its mismanagement by a partner.

By her teens, Sandra had learned to dig a well, fix a pickup, fire a rifle, tame a wild horse and dance the Texas two-step. She was a "cowgirl," a "simple cowgirl," as she said later, aspiring for most of her youth to be a cattle rancher.

Though life was isolated, her parents made sure there was plenty of intellectual stimulation. She once described a "race to the mailbox" for the books and magazines that would arrive at the Lazy B, including Time, the Saturday Evening Post and the National Geographic.

Her parents sent her for schooling at the Radford School for Girls in El Paso, where O'Connor lived with her grandmother. She was an excellent student, skipping two grades, but felt it necessary to veil her braininess. "In those days, it wasn't fashionable [for a girl] to get good grades," she said. "I tried not to have anybody know about it."

"The classes were small and the teachers were kind and caring," O'Connor wrote in her memoir. She especially remembered her dramatic arts teacher, who "insisted that I memorize various short essays and deliver them in public. These were frightening and painful experiences, but her insistence on proper and clear enunciation of the words and looking at the audience have stayed with me ever since." This was evident to anyone who has observed the precision and care of her questioning during Supreme Court oral arguments.

In 1946 she enrolled at Stanford University in Palo Alto at the age of 16. She studied economics, with the idea that the subject would help her manage the ranch. She graduated magna cum laude in 1950 and then enrolled in Stanford's Law School at the age of 20, finishing in two years rather than in the usual three.

"It's a little odd, the path I took," she would recall. "Because when I was young, I wanted to be a cattle rancher. That was what I knew and that was what I liked. And I went off to Stanford, I was pretty young and pretty naive. And I had a professor I really loved, who was himself a lawyer. And I thought one reason he was so effective was his legal background. And because of him, really, I applied to law school. I didn't know where it might lead or if I'd like it."

She was "ignorant and naive . . . about what life for a woman lawyer might be like . . . .It never occurred to me that there weren't women lawyers out there and that it might be hard to get a job as one. I never thought about that."

A member of the board of editors of the Stanford Law Review, Day graduated third in a class of 102, two places behind her future Supreme Court colleague William H. Rehnquist.

At the law school, she met John J. O'Connor III, who was in the class just behind her, whom she would marry. They now have three grown sons.

Despite her law school credentials, O'Connor would recount many times after her appointment her inability to get in the door, even for an interview, at a name law firm on the west coast.

"They were not hiring women," she said in an interview years later. "Although there were lots of notices placed on the bulletin boards at Stanford Law School, I contacted them and never got an interview. . . . It hadn't dawned on me. And finally I asked a woman friend of mine if she would ask her father, who was a major partner in a law firm, if he could arrange an interview for me" with the California firm of Gibson, Dunn, which he did.

She was determined to work and had little choice, as John needed the financial help to finish law school. She heard that the San Mateo (Ca.)County District Attorney had once hired a woman and so sought work there.

Informed that there were no openings, she pressed the District Attorney, offering to work for nothing, assuring him he would find her useful, promising to cause no trouble and to sit alone in a room with a secretary if necessary, which she did. So her first job paid nothing.

They settled in Phoenix, where he worked for a prestigious law firm while she opened up a small general practice out of a shopping center with another woman lawyer.

By then, she was the mother of one child expecting another. O'Connor traded her paid job for fulltime motherhood, hurling herself, on the side, into a whirlwind of suburban volunteer activity including work for the Arizona State Hospital, the Arizona State Bar, the Salvation Army, various local schools and, significantly, the Arizona Republican Party, where she volunteered in Barry Goldwater's 1964 presidential campaign and renewed her friendship with Rehnquist, then practicing law in Phoenix.

In 1965, she went back to work as an assistant attorney general in Arizona. When, in 1969, when state Sen. Isabel A. Burgess left Phoenix for Washington and an appointment to the National Transportation Safety Board, Arizona Gov. Jack Williams plucked O'Connor from the state attorney general's office and appointed her to Burgess' seat, to which she was elected in 1970 and ultimately chosen by fellow Republicans as their majority leader in the Senate.

She disliked legislative politics as much as politics apparently disliked her. At the end of her second full term, she resigned from the Senate for a judgeship in Maricopa County Superior Court. Many saw it as a step down for her, but it was a move toward an arena in which she would be more in control and less in the control of others.

She turned down urgent pleas from the party establishment to run for governor in 1978, despite the fact that she had grown tired, in the words of her son, Scott, of "all the shenanigans of the primary trial court level."

More to her taste was the offer, a year later, of a seat on the Arizona Court of Appeals. "It was so much more cerebral" than the lower court, says Scott. "You were dealing with an intellectual exercise rather than with circumstances beyond your control."

At a low point in Ronald Reagan's 1980 presidential campaign, when he and his aides were searching for a new issues, they came up with the idea of promising that his first appointment to the court would be a woman, according to Reagan biographer Lou Cannon.

He reminded his staff of his promise in February, 1981, when Justice Potter Stewart informed the administration that he would submit his resignation at the end of that Supreme Court term.

Then Attorney General William French Smith, and presidential aides Edwin Meese and Mike Deaver came up with a list of four women, including O'Connor. Her name had been mentioned by fellow Stanford graduates Rehnquist and William Baxter, then chief of the Justice Department's anti-trust division. Chief Justice Warren E. Burger spoke approvingly of her as well, citing an article she had published in the William and Mary Law Review in support of the principles of federalism in criminal law.

Reagan, Cannon reported, met her and was "charmed" by her, Cannon reports and never interviewed anyone else.

"I had a telephone call from then Attorney General Smith," O'Connor later said in an interview with National Public Radio's Nina Totenberg, "who asked me if I could come to Washington, D.C. to talk about a vacancy. He didn't say what kind of vacancy. I assumed it was a secretarial position of some sort," she joked, recalling that it was Smith's firm that had offered her such a job out of law school.

Of course, she conceded, she realized there was a vacancy on the court and that there was "already some talk" about her filling it," but she said she had not taken it seriously.

She met Smith and the next day met Reagan. "He was such a personable man. It didn't hurt that I had a ranch background . . . .So we found things to talk about right away"

"What an interesting day," she recalls thinking on the way back to Arizona.. "But thank goodness I don't have to go back and do that job."

Reagan made the announcement on July 7, 1981.

As a state appellate judge and before that, a state legislator, O'Connor's record was moderate, non-ideological and non-confrontational. Ultimately, as conservatives in the Republican party had feared during her confirmation process, that was also her profile as a Supreme Court justice.

Under ordinary circumstances, such an appointee might have made little difference to the law of the land. But circumstances were not ordinary in O'Connor's case. From the year of her arrival, the court would confront repeated challenges from the Reagan administration and its allies to established Warren and Burger Court precedents in the law of abortion, racial discrimination, criminal justice and church and state.

The court was being asked to overturn, or at least overhaul, the landscape of the law. More often than not, the court declined, choosing, instead, relatively modest change thanks in large measure to O'Connor's search for a middle ground between her more liberal and more conservative colleagues.

She was instrumental in relaxing, slightly, restrictions on the right to abortion and voted to uphold laws requiring parental notification for minors seeking to terminate pregnancy.

But she wielded her vote and her voice to stop the court from overturning the core holding of the landmark 1973 ruling in Roe v. Wade legalizing abortion.

"Liberty finds no refuge in a jurisprudence of doubt," she wrote for the majority in Planned Parenthood v. Casey in 1992. "Yet, 19 years after our holding that the Constitution protects a woman's right to terminate her pregnancy in its early stages, Roe v. Wade (1973), that definition of liberty is still questioned. We are led to conclude this: the essential holding of Roe v. Wade should be retained and once again reaffirmed."

In the field of criminal law, she was willing to ease, but not eliminate the Miranda rule barring the use of evidence obtained from a suspect not told of the right to remain silent and the right to counsel.

Writing for a majority in 1985, she allowed for an exception to the evidentiary rule for those occasions when police fail to warn suspects but act in good faith. "A simple failure [by police] to administer the warnings, unaccompanied by actual coercion," does not hopelessly taint evidence, she said.

But she declared that the court "in no way retreats from the bright-line rule of Miranda."

On affirmative action, she was once again the swing vote in the 2003 case upholding consideration of race in admissions policy at the University of Michigan Law school.

Following the principles set out 25 years ago by her mentor, the late Justice Lewis Powell, she wrote that "the court endorses Justice Powell's view that student body diversity is a compelling state interest that can justify using race in university admissions. . . . Race-based action necessary to further a compelling governmental interest does not violate the equal protection clause so long as it is narrowly tailored to further that interest."

"Effective participation by members of all racial and ethnic groups in the civic life of our nation is essential if the dream of one nation, indivisible, is to be realized," she wrote.

As a former state legislator, she was particularly vigilant in cases involving federalism- the balance between the powers of the states and of the Federal government.

In a 1992 case, she wrote the majority opinion striking down a federal law that effectively required the states to pass legislation for the disposal of radioactive waste.

"States are not mere political subdivisions of the United States," she wrote. "State governments are neither regional offices nor administrative agencies of the Federal Government. The positions occupied by state officials appear nowhere on the Federal Government's most detailed organizational chart. The Constitution instead "leaves to the several States a residuary and inviolable sovereignty."

"Whatever the outer limits of that sovereignty may be, one thing is clear: the Federal Government may not compel the States to enact or administer a federal regulatory program. . . ."

What "distinguishes her approach to judging," wrote conservative scholar and former Justice Department lawyer John Yoo, is "her effort to decide each case on its unique facts and context, her affinity for balancing the costs and benefits of a policy and her desire to leave issues open to be decided another day."

"Positioned exactly in the middle of a polarized nine-member Supreme Court," Yoo wrote, "O'Connor has provided the deciding fifth vote on some of the most controversial issues of our day. . . . If someone else had been appointed to her position on the court," he wrote, "our nation might now be living under different rules for abortion, affirmative action, race, religion in school and civil rights. We might well have a different president."

Some analysts have suggested that O'Connor's judicial methodology, by design or by effect, results in avoidance of hard answers to difficult questions.

Responding indirectly to this criticism to a Washington audience several years ago, O'Connor referred to a Papago Indian weaving in her chambers called, "The Man in the Maze."

"It's my favorite," she said, "because that's what life is after all. We're like the man walking in the maze. . . . You have to go this path or that, and you don't know what it's going to lead to, but you don't worry about it. You make the best choice you can and do the best job you can."

"There had been such interest in everything I did," O'Connor said, adding she was relieved when Ruth Bader Ginsburg became the second woman to join the court in 1993. "Both of us became just two of the nine justices."

O'Connor, who is sometimes described as bringing a woman's perspective to the court, said that while each judge brings personal experiences to the bench, another female judge said, "At the end of the day, a wise old woman and a wise old man will reach the same decision."