It began with a modest remark during a roundtable discussion with reporters: First lady Michelle Obama said she supports making it easier for mothers to breast-feed their babies, because “kids who are breast-fed longer have a lower tendency to be obese.”

Within days, the sentence — and a new Internal Revenue Service policy offering tax deductions for breast pumps — had touched off a political firestorm. Rep. Michelle Bachmann (R-Minn.) blasted the Obama administration for trying to impose a “nanny state” on mothers. Another potential 2012 presidential candidate, former Alaska governor Sarah Palin, mockingly said the first lady was trying to compensate for high milk prices. The East Wing withdrew, issuing a brief statement calling the subject “personal.”

For Mrs. Obama, the moment is a reminder that she will inevitably become more of a target as the 2012 campaign gets underway. After cultivating a non-controversial image as the “Mom in chief” over the past two years, she remains overwhelmingly popular with the public, yet even her most carefully planned moves will not be immune to political jabs.

But the incident goes well beyond the first lady — raising questions about health policy and the role of government. Should the tax code offer an incentive aimed at working mothers who pump breast milk and not at those who stay home or give their children formula? Are breast pumps any different from other routine medical items that qualify for tax deductions? Is breast-feeding truly better for children?

The discussion has both riveted and dismayed those involved in the breast-feeding issue. “We all expect this — we all know the Republicans and Democrats have their differences,” sighed Marsha Walker, a registered nurse who is executive director of the National Alliance for Breastfeeding Advocacy.

Referring to Bachmann, Walker said: “It’s not that she’s against breast-feeding. It’s that she’s using it as a vehicle of attack. And it’s unfortunate, because breast-feeding isn’t a political entity. It’s a public-health entity that doesn’t deserve to be used as political leverage.”

Much of the discussion centers not only around Obama’s remarks but also the new IRS rules, which were announced on Feb. 10 and will apply retroactively to devices purchased in 2010 and in the future. The tax authority found that breast pumps “are for the purpose of affecting a structure or function of the body of the lactating woman,” thus putting them in the category of a medical device.

Nursing mothers now have two options: If they have a medical flexible-spending account, they can potentially use pretax dollars to buy nursing supplies and breast pumps, which can run as much as $330 or more. Which devices will qualify will depend on each FSA’s rules.

If a woman does not have an FSA, she can itemize her taxes and deduct breast-feeding equipment costs, as long as her overall out-of-pocket medical costs exceed 7.5 percent of her income. Only about one-third of taxpayers itemize their taxes. In no case will breast-milk equipment receive a tax credit, the IRS said.

Nor is the federal government purchasing breast pumps for women, as Bachmann claimed. In an interview with conservative radio host Laura Ingraham, Bachmann said she gave birth to and breast-fed five children without government help and described the new policy as part of a liberal agenda.

“To think that government has to go out and buy my breast pump. . . . You want to talk about nanny state, I think we just got a new definition,” Bachmann said.

After her remarks drew attention, Bachmann added in a statement: “The issue is not breast feeding, but is rather Washington’s use of the tax code to tell people how to run their lives.”

According to an IRS spokeswoman, the new tax rules are similar to those men are permitted for a vasectomy. Men may use pretax dollars to pay for that surgery, or claim it as a medical expense.

The first lady has been criticized for launching a breast-feeding campaign, but there has been no campaign to speak of. She has sporadically commented on the subject in the past — including telling breast-feeding stories of her own — and said during the reporters’ roundtable that it will be incorporated into her larger work combating obesity.

“Kids who are breast-fed longer have a lower tendency to be obese,” she said. “We want to get into child-care centers, day-care centers, and start talking about how — what kind of snacks they’re getting there.”

Exactly how involved Obama might be is still unclear. Her office declined to elaborate on her plans, or to convey her opinion on the new IRS rules or Bachmann’s criticism.

“Breastfeeding is a very personal choice for every woman. We are trying to make it easier for those who choose to do it,” Mrs. Obama’s communications director, Kristina Schake, said in a statement. Her office said the “we” in the statement referred to the federal government, not specifically to the first lady.

The new IRS rules came after a group of Democratic members of Congress sent letters requesting the change. Still, at least one conservative group saw the first lady’s public statements as evidence that the administration is focused on aiding working mothers, not ones who stay home with their children.

“Giving tax breaks for breast pumps helps only those moms who are working outside the home and does nothing for us stay-at-home moms. This is consistent with President Obama’s pledge to increase the child-care tax credit as opposed to the child tax credit, incentivizing putting your kids in day care over any other child-rearing arrangement,”said Cathy Ruse, a senior legal fellow at the Family Research Council.

Palin, who like Bachmann also has five children, did not pursue whether the government should offer tax incentives for breast-feeding equipment. But she did take a crack at the reasons for the first lady’s interest.

“No wonder Michelle Obama is telling people to breast-feed their babies,” Palin said at an event on Long Island. “Yeah, you better, because the price of milk is so high right now.”

Nursing children are not generally given cow’s milk to replace breast milk, but instead drink baby formula.