Mrs. Obama told students at a high school graduation that Sotomayor is "more than ready" to be a justice and compared the judge's life story of humble beginnings and high achievement to the paths taken by her husband and herself.
Sotomayor, who grew up in a New York City housing project and went on to Princeton and Yale universities, "says she still looks over her shoulder and wonders if she measures up," Mrs. Obama said at Howard University, chiming in on Sotomayor's behalf as her husband began a Mideast trip.
It was a subtle but pointed counter to Republicans who have cited Sotomayor's speeches and writings about how her background affects her work as a judge to question whether she would let her personal biases interfere with her judicial decisions.
Hours earlier, Gingrich told supporters in a letter that he shouldn't have called Sotomayor a racist, adding that the word had been "perhaps too strong and direct." But he said the 2001 speech that prompted his remark, in which Sotomayor said she hoped the rulings of a "wise Latina" would be better than those of a white male without similar experiences, was still unacceptable.
Gingrich conceded that Sotomayor's rulings have "shown more caution and moderation" than her speeches and writings, but he said the 2001 comments "reveal a betrayal of a fundamental principle of the American system - that everyone is equal before the law."
Sotomayor, 54, would be the first Hispanic and the third woman to serve on the high court.
Gingrich's comments and similar ones by radio host Rush Limbaugh
who on Wednesday said Sotomayor would bring "racism" and "bigotry" to the court - have enraged Sotomayor's backers and caused problems for GOP figures who have been pushing to bring more diversity to the party.
Hispanic groups began a political push to force Republicans to denounce harshly worded criticism of Sotomayor, warning that their votes could depend on it.
"These gross mischaracterizations of Judge Sotomayor coupled with the deafening silence of the Republican leadership are leaving many within our community with a disturbing picture of the Republican Party. Much hangs in the balance, including our votes," said Janet Murguia, the president and CEO of the National Council of La Raza.
The White House, working with Democratic senators, hit back at GOP charges that Sotomayor would be an activist who legislates from the bench or a justice who allows her personal bias to interfere in legal decisions. Officials circulated talking points calling Sotomayor "a nonideological and restrained judge," citing conservatives who have praised her approach.
Wendy Long of the conservative Judicial Confirmation Network, a group leading the opposition to Sotomayor's confirmation, called the document "the biggest piece of fiction writing I have ever seen."
At the same time, Democratic senators circulated a 1994 speech in which Sotomayor spoke about how personal characteristics could affect judging, which Republicans never criticized during the 1997 debate on her confirmation to a federal appeals court - proof, the Democrats said, that conservatives are trying to politicize Sotomayor's nomination.
In 1994, Sotomayor said, "I would hope that a wise woman with the richness of her experiences would, more often than not, reach a better conclusion" than a wise man. "What is better?" she said. "I ... hope that better will mean a more compassionate, caring conclusion."
"No one made an issue out of Judge Sotomayor's comments the last time the Senate confirmed her for the federal bench, because everyone understood what she meant and knew her respect for the rule of law was unquestionable," said Sen. Chuck Schumer, D-N.Y., Sotomayor's home-state senator and her sponsor during the confirmation process.
Sotomayor returned to Capitol Hill on Wednesday for a second day of meetings with senators, staying mostly mum in public. She has used the visits to reassure Republicans and Democrats alike in private that while her background has shaped her worldview, she believes in following the law and wouldn't let her life experiences inappropriately influence her judgments.
But many Republicans sounded unconvinced.
"When I look at her ideology, record and philosophy, I'm deeply troubled," said Sen. Lindsey O. Graham, R-S.C., a member of the Judiciary Committee, after meeting with Sotomayor on Wednesday.
Graham said it's not fair to call the judge a racist, but that she has to prove to senators and the public "that, if they found themselves in litigation with a Latina woman ... that she would give you a fair shake."
Sotomayor visited 10 Republicans and Democrats as the leaders of the Judiciary Committee met separately but reached no deal on when her confirmation hearings should begin.
Sen. Patrick J. Leahy, D-Vt., the Judiciary Committee chairman, wants the process to begin next month, with the goal of holding a confirmation vote before Congress leaves in early August for a monthlong summer vacation. He's negotiating with the top Republican on the committee, Sen. Jeff Sessions of Alabama, who says he'd rather go slower in delving into Sotomayor's voluminous record of rulings during her 17 years as a federal judge, with hearings set for September.
Obama is pushing for a quicker timetable, hoping to spare Sotomayor the potential pitfalls of a drawn-out public debate on her confirmation during the customary August news lull. He also wants her seated in time to participate in discussions at the high court in September on which cases to hear when the session begins in October.