She's been called "extraordinary," "outstanding," "truly outstanding" and "the best thing since Girl Scout cookies." Speechmakers in the Senate called her appointment "historic," "truly historic," "a landmark" and "monumental."

It is just possible that sometimes Sandra D. O'Connor may not recognize the woman she reads about and sees on television so often these days. That is because her history and her testimony during her confirmation hearings suggest that she has arrived where she is by being relatively uncontroversial, by being low-keyed, by appreciating the fine detail rather than the cosmic sweep, by keeping out of trouble, rather than by making trouble.

Her achievements have been solid. But no one who knows them calls them brilliant or inspired. In that respect, she is no different than many other appointees to the U.S. Supreme Court.

And if she follows the example of many of them, it may be that she will not be heard from in any dramatic way for some time. She may burrow into the marble palace for months or years before making a mark. Then again, she could begin in a burst of glory. But that would not be her way.

The court, the late Chief Justice Harlan Fiske Stone once said, is "nine quiet old boys." Make that eight quiet men and one probably very quiet woman.

She appeared uncomfortable at the beginning. When she first came to town, she seemed visibly stunned, even a bit shaken, by all the attention she was getting. "I've never seen so many reporters, cameras, all in one place," she would say, smiling nervously through her teeth as she trekked from office to office paying courtesy calls on senators and refusing to answer even the most innocuous questions asked by the mob of reporters trailing her.

During the confirmation hearings, she said then, she would have much more to say.

Then came the confirmation hearings. But there, her favorite response to potentially controversial questions seemed to be that "it wouldn't be appropriate" to give her views.

To some extent, her reticence was traditional, designed in part to avoid prejudicing her future on the court and in part to avoid a controversy that might upset her confirmation. But it is also possible that this is her way.

One of her family's best friends, Arizona businessman Donald Myers, described her this way: "She is somebody who has run a middle-track down the road of reasonableness."

"She's not a colorful character," said Charles E. Ares, a University of Arizona law professor who has watched her career. "She's conventional. She exhibits all the traditional conservative traditions of lawyers: conservative in dress, conservative in demeanor and conservative in what she expects from the law."

She is, also, of course, the first woman justice on the Supreme Court. But her record, sponsoring bills eliminating gender distinctions in Arizona law, shunning championship of the Equal Rights Amendment, suggests that she believes in incremental progress, not great leaps forward.

She was disappointed, she said, not angry or bitter, when she couldn't find a job in a major law firm though she had ranked near the top of her graduating class at Stanford University Law School in 1952.

She is conservative on many social issues: abortion, school busing, the rights of criminal defendants, she indicated at her confirmation hearings, and she is clearly critical of the judicial "activism" of the Warren era at the Supreme Court.

But with equal conviction, O'Connor said she believes in leaving precedents alone for that is what brings order to the legal system.

All this will not stifle the fuss over her appointment. Attention will inevitably focus on the first question at the first oral argument by the first woman justice, the first vote by the first woman, the first opinion, the first dissent and the first mistake.

The court, up to now, has been a great male fortress, where the most prominent female was the statue "The Contemplation of Justice" at the main entrance.

The court's most famous previous encounter with a woman lawyer came in 1873, when the justices ruled 8 to 1 that the state of Illinois could exclude a woman from the practice of law because she was a woman.

"The natural and proper timidity and delicacy which belongs to the female sex evidently unfits it for many of the occupations of civil life," wrote concurring Justice Joseph P. Bradley.

Many women lawyers have tired of the hype surrounding the appointment. But few dispute its significance. "It's subtle," said Georgetown law professor Wendy Webster Williams. "It's important to have people whose life experience brings something to the court. It has been important to have someone who has grown up black in this country. Justice Thurgood Marshall has made a clear contribution.

"The same is true of women. It is important that she has had children, that she has interrupted her career to raise them, that she has faced exclusion because of it. It is an enriching perspective for the court."

The role model businesss "isn't a hype either," she said.

"I felt this kind of weird joy when the appointment was announced," said Williams, "and so did every other woman lawyer I know, even though some of them thought she'd be a disaster."

O'Connor's appointment comes at a time when young women are literally flooding the legal profession. When O'Connor graduated from law school, for example, fewer than 2.5 percent of the nation's lawyers were women. As of 1980, 7.5 percent were women, according to a recent American Bar Foundation study.

Women now constitute one third of the young lawyers, those 26 and under, which suggests that if the increase continues, well over half the nation's lawyers could be women by the year 2000.