WASHINGTON — A half-century after the advent of the birth control pill, the Obama administration on Monday ushered in a change in women’s health care potentially as transformative: coverage of birth control as prevention, with no copays.

Services ranging from breast pumps for new mothers to counseling on domestic violence were also included in the broad expansion of women’s preventive care under President Obama’s health care overhaul.

Since birth control is the most common drug prescribed to women, health plans should make sure it’s readily available, said Health and Human Services Secretary Kathleen Sebelius. “Not doing it would be like not covering flu shots,” she said.

Officials said the women’s prevention package will be available Jan. 1, 2013, in most cases, resulting in a slight overall increase in premiums. Tens of millions of women are expected to benefit initially, a number that is likely to grow with time. At first, some plans may be exempt due to an arcane provision of the health care law known as the “grandfather” clause. But those plans could face pressure from their members to include the new coverage.

Social and religious conservatives objected to the birth control mandate, saying a conscience exception unveiled by the administration is insufficient.

Sebelius acted after a near-unanimous recommendation last month from a panel of experts at the prestigious Institute of Medicine, which advises the government. Panel chairwoman Linda Rosenstock, dean of public health at the University of California, Los Angeles, said that prevention of unintended pregnancies is essential for the psychological, emotional and physical health of women.

“Over a span of generations from grandmothers to granddaughters, we have come from birth control being a hope and a wish – and almost luck – to being recognized as a part of health care that improves women’s health,” said Cynthia Pearson of the National Women’s Health Network, an advocacy group supporting the change.

As recently as the 1990s, many health insurance plans didn’t even cover birth control. Protests, court cases, and new state laws led to dramatic changes. Today, almost all plans cover prescription contraceptives – with varying copays. Medicaid, the health care program for low-income people, also covers birth control.

A government study last summer found that birth control use is virtually universal in the United States. Still, about half of all pregnancies are unplanned. Many are among women using some form of contraception, and forgetting to take the pill is a major reason.

Contraception can help make a woman’s next pregnancy healthier by spacing births far enough apart, generally 18 months to two years.

In a nod to social and religious conservatives, the rules issued Monday by Sebelius include a provision that would allow religious institutions to opt out of offering birth control coverage.

However, many conservatives are supporting legislation by Rep. Jeff Fortenberry, R-Neb., that would codify a range of exceptions to the new health care law on religious and conscience grounds.

“It’s a step in the right direction, but it’s not enough,” said Jeanne Monahan, a policy expert for the conservative Family Research Council.

As it now stands, she added, the conscience clause offers only a “fig leaf” of protection because it may not cover all faith-based organizations.