The ruling follows the Institute of Medicine's recommendation to treat birth control as preventive health because it promotes maternal and child health by allowing women to space their pregnancies. For religious-affiliated employers, the requirement will take effect in mid-2013.
Workplace health plans will have to cover all forms of contraception approved by the Food and Drug Administration, including the birth control pill, implantable devices, sterilization and the morning-after pill. There is no mandate to cover abortions.
Last Sunday, Catholic bishops in more than 140 dioceses issued denunciations of the decision that were read at weekend Masses.
Sister Carol Keehan, head of the Catholic Health Association — which supported Obama's 2010 health care law — summed up the feeling of some moderate Catholics who say political analysts are missing the point.
"It's not the issue of contraception but religious freedom," she said. "It's not about preventing women from buying anything themselves, but telling the church what it has to buy, and the potential for that to go further."
Wall Street Journal editorial writer Peggy Noonan said the contraception ruling might cost Obama the election.
But Jen Psaki, a former Obama aide, said millions of American women, including Catholics, see it differently.
"This is about one issue, and that is making sure all women, especially those who can't afford it, have access to health care," said Psaki, who is Catholic. "And if Mitt Romney and Newt Gingrich continue to make a political issue out of such an important human right, they risk jumping the shark with women voters of all political stripes."
Groups on the left and right raced into the debate.
Sen. John Cornyn, R-Texas, said he hopes the Obama administration "backs down on this rule that violates conscience. If not, we'll do everything in our power to repeal it."
NARAL Pro-Choice America defended the new ruling.
"This is one of the biggest victories for women's health in a generation," said Nancy Keenan, its president. "Nurses, janitorial staff and professors who work at colleges and universities that do not currently cover birth control will get access to contraception."
White House Press Secretary Jay Carney didn't say how employers' concerns might be addressed, though he said there were a lot of ideas for doing it.
He said Obama's focus is making sure that women employed by Catholic-affiliated employers like hospitals, colleges or charities are able to get contraception. At the same time, Carney said Obama wants to respect religious beliefs and convictions.
David Axelrod, a top political aide to Obama, hinted at possible adjustments to the rule or its application. He told MSNBC the administration didn't intend to "abridge anyone's religious freedom."
"This is an important issue," Axelrod said. "It's important for millions of women around the country. We want to resolve it in an appropriate way, and we're going to do that."
Santorum suggested this week that efforts to reach an accord won't be easy.
"The Catholic Church has been arguing and negotiating this for a year, and the administration is saying 'it's just a misunderstanding,'" Santorum said while campaigning in Colorado. "It's just a bunch of bull. They are folks who are trying to use their power to force people to do things that they believe they should do and are right. They don't care about their religion."
Speaking at a 2006 Call to Renewal conference, organized by the religious anti-poverty group Sojourners, Obama said secular Americans were wrong to ask churchgoers to "leave their religion at the door before entering the public square."
But Obama also said religious groups must be recognize "ground rules for collaboration" and the importance of the separation of church and state.
Associated Press writers Rachel Zoll in New York, Donna Cassata in Washington and Philip Elliott and Steve Peoples in Colorado contributed to this report.