A piece of federal legislation intended to help religious Americans in the workplace has prompted Senator Kerry of Massachusetts to join forces with one of his most conservative political adversaries – and is causing a falling-out among liberal groups that often march in lockstep.

The Workplace Religious Freedom Act would require employers to accommodate workers’ religious observance or principles unless the accommodation would cause “significant difficulty or expense.”

The bill protects employees who choose to wear religious garb, or who need time off on certain days, as well as religious practices that have “temporary or tangential impact” on work duties.

The primary sponsor of the legislation is Senator Santorum of Pennsylvania, a Republican. Mr. Kerry, the likely Democratic nominee for president, is the lead co-sponsor.

One of the main proponents of the bill, Nathan Diament of the Orthodox Union, called the two senators “an odd couple.” Mr. Diament said he believes the presidential campaign has helped advance the legislation.

“It’s got Santorum and Kerry, who are in positions of leadership in their respective parties. You have both par ties sort of vying for the attention and support of religious communities,” Mr. Diament said.

The legislation has received support from lawmakers across the political spectrum. Senators Clinton and Schumer, both Democrats, are co-sponsors of the measure. So is Senator Hatch of Utah, a Republican.

An impressive and diverse lineup of organizations is also backing the religious accommodation bill. They include the American Jewish Committee, the Anti Defamation League, and the Traditional Values Coalition. Religious leaders from nearly all faiths are on board, including evangelical Christians, Muslims, Sikhs, and even Scientologists.

Despite the broad coalition, the legislation has made little headway. Mr. Kerry and Senator Coats of Indiana put forward the first version of the bill seven years ago. It never made it out of committee.

“This has been sort of a feel-good, motherhood and apple pie kind of idea which we’ve always gotten a good reception for, but which has never had that kind of galvanizing energy,” Mr. Diament said.

Advocates for the bill hoped this presidential election year would be different. Plans were afoot to attach the legislation to a class-action reform bill that was expected to move through the Senate. There was even talk of the religious accommodation measure passing by unanimous consent.

But on June 2,the American Civil Liberties Union sent a 12-page letter to Senate offices expressing its strong opposition to the bill. The group warned that in its current form the bill “would threaten important rights of religious minorities, women, gay men and lesbians, and persons seeking reproductive health care and mental health services.”

One danger, the ACLU said, was that workers could use their religious beliefs to temporarily stop work or to refuse to work with customers or colleagues on account of their gender or sexual orientation. The ACLU said some nurses have claimed that they could not join in emergency surgery that might cause harm to an unborn fetus.

“The cases we’re speaking about are really emergency situations. In one case a woman was literally left standing in a pool of her own blood,” said an ACLU lobbyist, Christopher Anders.

Mr. Anders said some pharmacists have refused, on similar grounds, to fill prescriptions for the so-called morning after pill. Under the Santorum-Kerry bill, a woman looking for such medicine might be turned away.

The ACLU also contends that the bill could allow employees who cite a religious belief to decline to work with homosexual colleagues or with members of the opposite sex.

“This really undermines any place where employers have gone beyond the bare minimum of what federal civil rights laws require,” Mr. Anders said.

The ACLU’s position has garnered some support. Women’s groups and abortion rights organizations, such as Planned Parenthood, have weighed in against the bill. Americans United for Separation of Church and State and the American Humanist Association have expressed concerns that the bill would allow more proselytizing in the workplace.

The only major Jewish group to take a stance against the legislation is the National Council of Jewish Women.

“This was a very difficult decision because we are closely allied with people on both sides of the issue,” said the group’s president, Marsha Atkind.

“Our concern is that a policeman who’s protecting a gay facility or an abortion clinic can refuse to do so. He could easily say that’s tangential and temporary,” she said. “That’s the part that troubles us.”

Ms. Atkind said her council is pushing for a compromise between the civil liberties organizations and the religious groups.

The ACLU has suggested that religious attire and days-off provisions be maintained and that the more problematic language be scrapped.

Mr. Diament of the Orthodox Union said he was not inclined to back a change in wording of the bill. He called the ACLU’s warnings “baseless.”

“They’re spinning out ideas of a parade of horribles which even those in our coalition who have identical views on abortion and gay-rights issues think are far-fetched and will not come to pass,” Mr. Diament said. He said that a similar law that is already on the books in the New York has not led to problems.

Mr. Diament accused the civil liberties group of drifting from its roots. “I think the ACLU is inhabiting a world of political correctness. They seem to think if something is going to benefit religious people in America, it’s somehow going to come at the cost of abortion and gay rights that they seem to now feel is more important than every other fundamental right that America has cherished for years and years,” he said.

Mr. Anders said the ACLU still supports broad religious freedom, with the caveat that the exercise of that right not hurt others.

“We historically have never supported one person’s religious claim harming anyone else,” he said.

A spokesman for Mr. Kerry’s Senate office, Andrew Davis, said no one was available to discuss the bill in detail yesterday. He provided a reporter with a 1997 statement of Mr. Kerry’s about an earlier version of the bill.

Mr. Kerry said he was moved to sponsor the legislation after workers at a dog track in Massachusetts were fired for refusing to work on Christmas Day. “When I picked up the newspaper and read about this, I was dumbfounded,” he said. The senator called the refusal to accommodate the workers “a form of discrimination that is unacceptable.”

Asked about Mr. Kerry’s plans for the bill, Mr. Davis said, “It’s something he’d like to see passed.”

Mr. Anders said the objections of his group and others have caused some senators to back away from the measure.

Mr. Diament said Mr. Kerry has “remained solid” in his support for the bill. Mr. Diament said he was “still optimistic” about passing the legislation this year, though he acknowledged that time is running short.

Another significant obstacle to the bill is the opposition of business leaders.

“There are a lot of employers who just don’t want this thing,” said Lawrence Lorber, an employment law attorney who testified against an earlier version of the bill on behalf of the U.S. Chamber of Commerce. He said employers are already required to make minor accommodations for employees’ religious preferences.

Mr. Lorber said the legal profession is one business that would benefit if the proposed law passes. “Employment litigation is one of the great growth industries,” he said. “You’re going to see a whole bunch of strange litigation.”