The so-called war on women escalated Thursday onto a new front, after a Democratic strategist and cable-television pundit declared that Ann Romney, the stay-at-home, mother-of-five wife of the presumptive GOP presidential nominee, had “never worked a day in her life.”

This time, however, Republicans were on the offensive. And after weeks of hammering Romney and the Republicans on gender-related issues, including contraception coverage and equal pay for women, President Obama’s forces were thrown on defense.

Taking to the social media Web site Twitter, where the gaffe had grown into a firestorm, top Obama campaign officials scrambled to distance themselves from the comments on CNN by Hilary Rosen, a political and public relations consultant who is a business associate of former White House communications director Anita Dunn.

Even first lady Michelle Obama weighed in on Twitter, writing: “Every mother works hard, and every woman deserves to be respected. –mo.”

Mitt Romney’s campaign, which is struggling to close a double-digit deficit with female voters, seized upon the comment. It evoked a decades-old debate — once dubbed the “Mommy Wars” — about whether mothers who can afford to stay home should work outside it.

Within two hours of Rosen’s comment, Ann Romney had issued her first tweet ever: “I made a choice to stay home and raise five boys. Believe me, it was hard work.”

The Romney campaign also organized a conference call in which some of its prominent female backers used Rosen’s comments as an opening to denounce the president.

“This administration would do well to stop disrespecting stay-at-home moms and listen to them,” said Penny Nance, president of the conservative organization Concerned Women for America. But when pressed by reporters for examples of the president or his administration showing disrespect for mothers who work at home, the Romney surrogates did not provide any specific examples.

Rosen made several attempts to defend her comments on Twitter, saying that she admired Ann Romney but was trying to point out that the candidate’s wife — often cited by Mitt Romney as his sounding board on women’s concerns — has not experienced the economic struggles that many working mothers face.

Later, Rosen apologized in a statement, in which she said: “As a mom I know that raising children is the hardest job there is. As a pundit, I know my words on CNN last night were poorly chosen.”

The contretemps knocked the White House off-message on a day that it had hoped to devote to the economy, and specifically to pushing the idea of raising taxes on millionaires.

The president had scheduled a series of interviews with local television outlets in swing states to push the proposal, but he also had to address Rosen’s comments.

“There’s no tougher job than being a mom. When I think about what Michelle had to do, when I think about my own mom, a single mom who raised me and my sister — that’s work,” Obama told the ABC affiliate in Cedar Rapids, Iowa. “Anyone who would argue otherwise probably needs to rethink their statement. More broadly, I don’t have a lot of patience for commentary about spouses of political candidates.”

The episode was the mirror image of a controversy 20 years ago, when the spouse of another presidential contender found herself under fire for the life choices that she had made.

“I suppose I could have stayed home and baked cookies and had teas, but what I decided to do was fulfill my profession, which I entered before my husband was in public life,” lawyer and Arkansas first lady Hillary Rodham Clinton said at the time.

This time, it was Ann Romney’s turn to defend her decisions.

“Other women make other choices, to have a career and raise family, which I think Hilary Rosen has actually done herself. I respect that, that’s wonderful,” she said Thursday on Fox News. “But, you know, there are other people that have a choice. We have to respect women and all those choices that they make. And, by the way, let me give a shout out to all the dads that are at home raising kids.”

On Thursday, a Romney aide said that when their five sons were growing up, the family had no nannies, no cooks and a once-a-week housecleaner.

Early in Mitt Romney’s political career, their most traditional of marriages had been mocked — especially after his wife told the Boston Globe in 1994 that the pair had never had a “serious argument,” and that he had never raised his voice to her. If he had, she added, “I’d dissolve into tears.”

In that same interview, during her husband’s unsuccessful campaign for the Senate, Ann Romney gave an impolitic description of the closest thing to economic stress they couple had ever experienced. When her husband was in graduate school, she said, “we had no income except the stock we were chipping away at. We were living on the edge, not entertaining.”

Today, the judgmentalism of working mothers no longer rages as it once did. In this economic climate, fewer have the option to forgo a paycheck in favor of staying at home with their children. As of March, a near-record 57.7 percent of women 16 and older — 72.5 million in all — were in the labor force, according to the Bureau of Labor Statistics.

But even among those who are working by choice, rare is the mother who has not wondered at some point whether it would be better for her children if she were home, more or all the time, even if it meant a smaller house, fewer vacations or public school.

“It’s hard not to second-guess our choices, especially for our generation,” said Joanne Bamberger, a writer, blogger and non-practicing lawyer in Chevy Chase who describes herself as a “work-at-home mom.”

Another reason that Republicans were quick to cry foul was the fact that Ann Romney has become a poised and popular figure on the campaign trail, exuding a warmth that her husband often lacks.

“This has done more to humanize the whole Romney effort than anything the Romney campaign has done to date,” said Republican pollster Linda DiVall. “Thank you, Hilary.”

Indeed, one of the few areas where no one has questioned Mitt Romney’s authenticity is in his devotion to his wife.

When he was running the Salt Lake City Olympics in 2002, Mitt Romney nominated Ann — then gaining her strength back after her diagnosis of multiple sclerosis — to run part of the torch relay as a “local hero.”

“It was an amazing thing to be too weak to barely walk when we got out there, and to be strong enough after three years, to have my children helping me to hold my arm up, and my husband was at my elbow, running with me and running the torch into Salt Lake City, as his hero,” Ann Romney later recalled, according to a biography of her husband written by Boston Globe reporters Michael Kranish and Scott Helman.

These days, however, Romney often cites his wife when he is asked about his knowledge of what is on women’s minds.

In an address to newspaper editors and reporters last week, for instance, the former Massachusetts governor said: “My wife has the occasion, as you know, to campaign on her own and also with me, and she reports to me regularly that the issue women care about most is the economy.”

Staff writer David Nakamura and research editor Alice Crites contributed to this report.