WASHINGTON — US Republicans on Wednesday escalated their election-year attacks on President Barack Obama in a feud over health insurance coverage of birth control, accusing him of a "systematic" assault on religion.

Republican House Speaker John Boehner charged a new rule that most employers -- including church-affiliated entities -- must cover contraception for women "constitutes an unambiguous attack on religious freedom in our country."

Boehner vowed in a fiery speech that lawmakers would roll back the regulation if Obama fails to reverse it, warning: "This attack by the federal government on religious freedom in our country must not stand, and will not stand."

The assault, echoed by leading Senate Republicans, seemed designed to make Obama and his Democratic allies pay a political price -- notably among Catholic swing voters in battleground states vital to his reelection in November.

But a brace of new polls show a majority of Catholics -- and the US public at large -- support the president's position, which has drawn heavy fire from some of the church's largest groups because contraception is against its teachings.

The fight erupted when Obama decided not to exempt religious employers -- apart from houses of worship -- from a requirement under his health reform law that work-based insurance plans offer women coverage for contraception.

Republican Senator John Thune accused the president of "trampling" constitutional protections for freedom of worship and railed against "a systematic dismantling of religious liberty for people in this country."

Republican Senator Kelly Ayotte called the new requirement an "unprecedented affront to religious liberty" and insisted "this is not a womens' rights issue, this is a religious liberty issue."

"It's an affront to what we stand for as Americans," she said at a press conference with Thune, Republican Senate Minority Leader Mitch McConnell, and Republican Senators Marco Rubio and Roy Blunt.

The assault mirrored other Republican attacks anchored on portraying Obama as somehow un-American, notably Republican presidential candidate Mitt Romney's charge that the president aims to refashion the United States as a European welfare state.

"We must have a president who is willing to protect America?s first right, a right to worship God, according to the dictates of our own conscience," said Romney, who has labored to shore up his standing with conservatives.

"This is, I think, ironic, that Mitt Romney is ... criticizing the president for pursuing a policy that's virtually identical to the one that was in place when he was governor of Massachusetts," Obama spokesman Jay Carney shot back.

Still, Carney said at his daily briefing, Obama is "very sensitive to concerns like these" about the rule and "wants to find a way to implement it that can allay some of the concerns that have been expressed."

US Health and Human Services Secretary Kathleen Sebelius rolled out the new rules in late January, saying that "very careful consideration" had been given to "the important concerns some have raised about religious liberty."

The move, brought in under Obama's landmark health care reform law, offers an exemption for churches and other houses of worship -- a carve-out that Democrats note is absent from similar laws in eight of the 28 states that have them.

Other religious groups can qualify for a one-year exemption before they are covered by the new measures until August 2013 when they will have to comply with the law.

Sebelius said when she announced the new procedures that they struck "the appropriate balance between respecting religious freedom and increasing access to important preventive services."

The final rule, which followed an interim decision announced in August 2011, was applauded by women's rights advocates but denounced by the US Conference of Catholic Bishops and political conservatives.

Some commentators have suggested any loss of support among Catholics could be balanced by support for the measures among women voters and the young -- groups Obama needs to win reelection.