SALT LAKE CITY, Feb. 3 — Faith's domain is evident everywhere at the Utah Legislature, where about 90 percent of the elected officials are members of the Church of Jesus Christ of Latter-day Saints. Prayers are commonplace, and lawmakers speak of their relationship with God in ordinary conversation.

So it might be tempting to assume that legislation relating to the divisive national debate about the teaching of evolution in public schools would have a predictable outcome here.

Senate Bill 96 is proving that assumption wrong. The bill, which would require science teachers to offer a disclaimer when introducing lessons on evolution — namely, that not all scientists agree on the origins of life — has deeply divided lawmakers. Some leaders in both parties have announced their opposition to the bill, and most lawmakers say that with less than a month left in the legislative session, its fate remains a tossup.

One of the reasons why is State Representative Stephen H. Urquhart, a Republican from southern Utah whose job as majority whip is to line up votes in his party. Mr. Urquhart announced last week that he would vote against the bill.

"I don't think God has an argument with science," said Mr. Urquhart, who was a biology major in college and now practices law.

Mr. Urquhart says he objects to the bill in part because it raises questions about the validity of evolution, and in part because the measure threatens traditional religious belief by blurring the lines between faith and science.

Supporters of the bill, which passed the Senate on a 16-to-12 vote one day before Mr. Urquhart's announcement, still predict that it will pass in the House. They say the bill is not about religion, but science. Gov. Jon Huntsman Jr., a Republican and former Mormon missionary, has not said what he will do if the bill reaches his desk.

"I don't have to talk about religion — it's of no meaning and it's not part of this discussion," said State Representative James A. Ferrin, a Republican and the sponsor of the bill in the House. "It's not about belief, it's about not overstepping what we know."

Opponents of the bill, including State Senator Peter C. Knudson, the Republican majority leader, openly laugh at talk like that.

"Of course it's about religion," Mr. Knudson said.

He and other lawmakers say that part of the debate here is in fact over what kind of religion would be buttressed by the legislation. Although the Origins of Life bill, as it is formally known, does not mention an alternative theory to evolution, some legislators say they think that voting yes could be tantamount to supporting intelligent design, which posits an undefined intelligence lurking behind the miracles of life and which differs greatly from the Mormon creation story.

"There are people who say, 'That's not my religion,' or that it will only confuse our children," said State Representative Brad King, a Democrat and the minority whip in the House, who also plans to vote against the bill. "For me, it's sort of that way," added Mr. King, whose father, a Mormon bishop, taught evolution at the College of Eastern Utah.

Others say that Mormonism, with its emphasis that all beings can progress toward higher planes of existence, before and after death, has an almost built-in receptivity toward evolutionary thought that other religions might lack. Still others oppose the state's inserting itself in matters of curriculum, which are mostly under the control of local school districts.

Advocacy groups who follow the battle over the teaching of evolution nationally say that what happens here could be important far beyond state borders.

"It's being watched very closely because of the very conservative nature of the state," said the Rev. Barry W. Lynn, the executive director of Americans United for Separation of Church and State, based in Washington. "If the legislation is rejected in Utah, it would be a very strong signal that the issue should be avoided elsewhere."

Missouri's legislature is considering a bill requiring "critical analysis" in teaching evolution. An Indiana lawmaker has called evolution a type of religion and proposed a bill banning textbooks that contain "fraudulent information."

Gov. Ernie Fletcher of Kentucky, a Republican, pointed out in his State of the State address earlier this month that alternative explanations for the origins of species can already be taught in Kentucky schools. A spokesman for Mr. Fletcher said he was not advocating alternatives to evolution, but merely pointing out the options.

The Utah bill's main sponsor, State Senator D. Chris Buttars, a Republican from the Salt Lake City suburbs, said he was not surprised by the debate it had inspired. He said ordinary voters were deeply concerned about the teaching of evolution.

"I got tired of people calling me and saying, 'Why is my kid coming home from high school and saying his biology teacher told him he evolved from a chimpanzee?' " Mr. Buttars said.

Evolutionary theory does not say that humans evolved from chimpanzees or from any existing species, but rather that common ancestors gave rise to multiple species and that natural selection — in which the creatures best adapted to an environment pass their genes to the next generation — was the means by which divergence occurred over time. All modern biology is based on the theory, and within the scientific community, at least, there is no controversy about it.

Even so, one important supporter of the bill, State Representative Margaret Dayton, a Republican and chairwoman of the House Education Committee, said her convictions had been underlined in recent days. "A number of scientists have been in touch with me, and I can verify that not all scientists agree," Ms. Dayton said.

Utah's predominant faith has also made its stance less predictable on other issues touching on religion in school — notably school prayer. Enthusiasm for the idea has been muted or ambivalent, said Kirk Jowers, a professor of political science and director of the Hinckley Institute of Politics at the University of Utah. Professor Jowers pointed to the awareness among Mormons of their religion's minority status in the nation and world.

"It was kind of a realization that if you push to have prayer in school, then outside of Utah, the prayer would not typically be a Mormon's prayer, so is that road you want go down?" Professor Jowers said.

Katie Kelley contributed reporting from Denver for this article.