The reshuffling of President Obama’s Cabinet gained speed Wednesday when Labor Secretary Hilda L. Solis announced her resignation, but White House
officials said three others, including Attorney General Eric H. Holder Jr., would remain in their jobs.

Obama hailed Solis, who presided over a period of high unemployment, as “a tireless champion for working families” during “the worst economic downturn since the Great Depression.” In a statement Wednesday, the president said that “her efforts have helped train workers for the jobs of the future, protect workers’ health and safety and put millions of Americans back to work.”

Solis had been the first, and only, Hispanic woman in a top Cabinet post. Her resignation, following the resignation of Environmental Protection Agency Administrator Lisa P. Jackson and the withdrawal of Susan E. Rice from consideration for secretary of state, intensifies debate over racial and gender diversity in Obama’s second-term Cabinet and among his top appointees.

Obama has been restocking the Cabinet ahead of his inauguration, unveiling nominees this week to lead the Defense Department and Central Intelligence Agency. On Thursday, he is expected to nominate White House Chief of Staff Jack Lew to be Treasury secretary. Earlier, he named Sen. John F. Kerry (D-Mass.) as his choice for secretary of state. All four nominees are white men.

White House aides said that Holder, Health and Human Services Secretary Kathleen Sebelius and Veterans Affairs Secretary Eric K. Shinseki would remain in their posts. People familiar with Holder’s thinking said he does not expect to stay in office for Obama’s entire second term, and perhaps for only a few months.

Obama relied heavily on support from women and minority groups in the election, and some supporters have voiced concern about a lack of women in Cabinet jobs. But White House press secretary Jay Carney defended the president’s hiring record Wednesday, saying that Obama believes “diversity is important.”

“Women are well represented here in the president’s senior staff,” Carney said. “These stories are in reaction to a couple of appointments.” He suggested waiting to see the “totality” of the president’s second-term Cabinet.

Solis had been widely expected to resign to run for office in Los Angeles, most likely for a seat on the powerful Los Angeles County Board of Supervisors.

In an interview at a Washington Post Live event in December, Solis recalled that a high school counselor “told me that I was not college material and that I should lower my sights and stay a secretary. Thirty years later, I can say my title is secretary of labor.”

Solis has defended the administration’s record on job creation despite a stubbornly high unemployment rate that stands at 7.8 percent nationwide and is far higher for African Americans and Hispanics.

She has also come under criticism from some coal-mine safety experts for failing to shake up the department’s Mine Safety and Health Administration or to implement effective new regulations in the wake of the Upper Big Branch coal mine explosion in West Virginia, which killed 29 workers in 2010.

News of Solis’s resignation prompted praise for her from Democrats and labor leaders.

AFL-CIO President Richard Trumka issued a statement saying that Solis, who came from a blue-collar family, had “brought urgently needed change” to the Labor Department. He said that, under her, the department “talks tough and acts tough on enforcement, workplace safety, wage and hour violations and so many other vital services.”

Sari Horwitz and Al Kamen contributed to this report.