WASHINGTON — President Barack Obama's top ally in the US Senate on Thursday condemned as "senseless" an angry spat over a White House plan to require most insurance plans to cover birth control for women.

"That is so senseless," Democratic Senate Majority Leader Harry Reid said as Obama's Republican foes sought vainly to force a vote on a measure assailing the proposed rule, which was drawn heavy fire from some religious groups.

"This debate that's going on dealing... with contraception is a rule that hasn't been made final yet," said Reid. "Everybody should calm down."

His comments came as the White House sought a way to quell the political firestorm, which has seen a rebellion from Democrats from key states where Catholic swing voters will be crucial in the November elections.

Republicans, seizing an opportunity to hammer the White House, have accused Obama of waging war on religious freedom with his proposal to require some church-affiliated entities to provide insurance that covers contraception for women, as well as other reproductive health services.

Democrats "won't allow those of us who are sworn to uphold the US Constitution to even offer an amendment that says we believe in our first amendment right to religious freedom," complained Republican Senate Minority Leader Mitch McConnell.

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 and some parochial schools -- from a requirement set under his landmark health reform law.

The White House, seemingly caught flat-footed by the uproar, has said it hopes to find a compromise.