WASHINGTON - As the U.S. Supreme Court's third female member, Elena Kagan would bring a shift laden with symbolism, and perhaps substance.

Her Senate confirmation would put women in three of the nine chairs for the first time. Twenty-nine years after Sandra Day O'Connor broke the court's gender barrier, women's representation on the court would nearly match their percentage in the legal profession.

Studies suggest the appointment of a third female director can change a corporate board's dynamics, and women's advocates say they hope Kagan, 50, would have a similar effect, burying the perception and reality of the court as a male-dominated enclave.

"What we have seen repeatedly with two women on the Supreme Court is that they are seen as exceptions to the rule," said Marcia Greenberger, copresident of the National Women's Law Center. Kagan's appointment, she said, moves "toward the day when it's accepted that women are just as likely as men to be on the Supreme Court."

Only a year ago, the court had just one woman, Ruth Bader Ginsburg, who in 2007 told USA Today that she was "lonely" after O'Connor's retirement the previous year.

President Obama doubled that number last year by choosing Sonia Sotomayor. With Kagan's selection, he became the first president to nominate two women to the court.

The prospect of three female justices was "appealing" to Obama, said senior adviser David Axelrod: "It helps make the court a more representative body."

O'Connor told ABC's Good Morning America this month that three women on the court could make a big difference, saying, "That's much better than one or two."

A 2009 Supreme Court case highlighted the difference even one female justice can make. The case concerned a 13-year-old girl who had been ordered to strip to her underwear so school officials could search her for prescription drugs.

During arguments, Justice Stephen G. Breyer wondered aloud whether a strip search was such a traumatic event for students who change clothes in front of others for gym class. Ginsburg bristled, saying the girl had been asked to shake out her bra and waistband.

Ginsburg later told USA Today that some of her colleagues didn't appreciate how humiliating the incident might have been.

"They have never been a 13-year-old girl," she said. "It's a very sensitive age for a girl. I didn't think that my colleagues, some of them, quite understood."

By the end of the court's term, Breyer and a majority of the court had come around to Ginsburg's view, ruling, 8-1, that officials had violated the girl's constitutional rights.

Whether that case is more than an isolated example is a matter of dispute. Most Supreme Court cases don't directly involve issues of gender. That leads some people, including Roger Clegg, president of the Center for Equal Opportunity, to question whether sex is a legitimate consideration in selecting a justice.

"Even if, once in a great while, there comes along a case where being a woman provides some particular insight, does that justify choosing someone other than the most qualified person, who will be sitting on all the cases?" asked Clegg, whose group fights racial preferences.

In the corporate world, having women on boards makes a difference, according to a 2006 study by researchers led by Vicki W. Kramer, a Philadelphia organizational consultant.

The study, based on interviews with chief executive officers, corporate secretaries, and female directors, found that boards with women were more likely to think about the broad implications of company actions, considering not just shareholders but also employees, customers, and the community.

The effect that women had depended on their numbers, it found. Lone female directors reported that they felt isolated and were often perceived as representatives of their gender. That only partly disappeared with the addition of a second woman.

But adding a third woman created the "critical mass" necessary to put the female directors on the same plane as their colleagues, the study found. "With three, they just began to become members of the board," Kramer said.

The Supreme Court accepted the "critical mass" reasoning in 2003 when it upheld the University of Michigan's use of race in law school admissions. Michigan argued that increased black and Hispanic enrollment would overcome tokenism.

The winning lawyer in that case, Maureen Mahoney of Latham & Watkins L.L.P. in Washington, questions whether the "critical mass" concept applies to a Supreme Court that would include Ginsburg, Sotomayor, and Kagan.

"These are people who have already achieved the pinnacle of success in our profession," Mahoney said.

She called the selection of a third female justice "a great benchmark of women's professional progress in America," but "I don't think it's going to be any kind of a sea change in the way the court works."