Obama launched a spirited defense of the Affordable Care Act on Friday, telling a mostly female audience at the White House that he and his allies “are going to keep fighting with everything we’ve got . . . to make sure that every American gets the care that they need when they need it, at a price that they can afford.”

The East Room speech marked the start of a concerted campaign by the White House and several advocacy groups to enroll tens of millions of uninsured Americans in private plans starting Oct. 1. Citing Mother’s Day, the president touted that women get new benefits under the law, including full coverage of mammograms.

Flanked by more than a dozen women who had written him to describe how the new health-care law had changed their lives, the president told stories of mothers such as Carol Metcalf, who no longer worry that their children won’t be able to obtain insurance because of preexisting conditions, and Natoma Canfield, a self-employed business owner who nearly faced catastrophe because she stopped paying her premiums right before having a cancer relapse.

Obama acknowledged that the law continues to come under attack, saying: “There are times where I just want people to step back and say, are you really prepared to say that 30 million Americans out here shouldn’t have health insurance? Are you really prepared to say that’s not a worthy goal, because of politics?”

The administration and its allies acknowledge they face a major challenge in implementing the law: Last month, a Kaiser Family Foundation poll found that 42 percent of Americans were unaware that it was in effect, with 12 percent under the impression that Congress had repealed it. Facing a constrained budget, Health and Human Services Secretary Kathleen Sebelius has appealed to health-industry executives to help fund public outreach efforts.

Michael Tanner, a senior fellow at the libertarian Cato Institute, said the president was “trying to put lipstick on a pig” by touting a measure that will raise insurance costs for consumers. Tanner said young, uninsured Americans — whose enrollment would help contain overall costs because they file fewer claims — would be better off waiting to sign up once they experience illness.

But the president said the law’s critics are spreading misinformation.

“Don’t let people confuse you. Don’t let them run the okey-doke on you,” he said, the old-fashioned phrase prompting laughter from the crowd. “Don’t be bamboozled.”

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