SAN FRANCISCO — A California congressman is breaking a longstanding taboo by declaring himself a nonbeliever.

Fortney “Pete” Stark Jr., an 18-term Democratic veteran of the House, made the unusual declaration after being queried by secular groups running a contest to find the highest-ranking atheist in American politics.

“When the Secular Coalition asked me to complete a survey on my religious beliefs, I indicated I am a Unitarian who does not believe in a supreme being,” Mr. Stark, 75, said in an statement emailed to The New York Sun.

Atheist groups hailed Mr. Stark yesterday as the first member of Congress to declare that he does not believe in God. “With Stark’s courageous public announcement of his nontheism, it is our hope that he will become an inspiration for others who have hidden their conclusions for too long,” the executive director of the American Humanist Association, Roy Speckhardt, said.

Mr. Stark’s declaration notwithstanding, the contest sponsored by the Secular Coalition of America hardly had politicians clamoring to embrace nonbelief. A spokeswoman for the group, Lori Lipman Brown, said 47 people entered to win $1,000 by identifying the highest-ranking politician who is an atheist. The only other politicians willing to identify themselves as nonbelievers were two school board members and one town meeting member. Aside from Mr. Stark, no state or federal official at any level agreed to be named as an atheist.

“That looks rather distressing, especially if we count 30 million people, or 10% of Americans, as nonbelievers,” Ms. Brown said, citing figures from opinion polls. Still, she said she was “not at all surprised” that so few politicians said they were nonbelievers. “That could be political suicide,” Ms. Brown, a former Nevada state senator, said.

Ms. Brown pointed to a recent USA Today/Gallup Poll that found 53% of Americans would not consider voting for an atheist presidential candidate. Homosexuals, the repeatedly divorced, Jews, Mormons, Catholics, and women all fared better, with a majority of Americans willing to consider them as candidates. “People who don’t believe in God are the most distrusted minority in the United States,” she said.

The Senate’s official historian, Donald Ritchie, said he thought the claim that Mr. Stark was the first avowed nonbeliever in Congress was probably correct.

“A lot of them don’t list an affiliation but they don’t say they don’t believe or they’re not religious,” Mr. Ritchie said. “We’ve never had a Madalyn Murray O’Hair-type up here, somebody who made a crusade of it.”

Mr. Stark’s press secretary, Yoni Cohen, said the congressman was not available for an interview yesterday. Mr. Stark’s statement suggested that he disclosed his religious views to promote the separation of church and state and to “stop the promotion of narrow religious beliefs in science, marriage contracts, the military and the provision of social services.”

Mr. Stark, whose district covers suburban and rural areas southeast of Oakland, is one of the most liberal Democrats in Congress. Last year, he got a 95% score from Americans for Democratic Action. His voting record has caused concern among some pro-Israel activists.

During Israel’s war with Hezbollah last summer, he was one of only eight members of Congress to vote against a resolution backing Israel and condemning Hamas and Hezbollah.

A blogger who discussed the issue with Mr. Stark, Amos Bitzan, said the congressman opposed the measure because he viewed it as unreasonably skewed toward Israel. However, Mr. Bitzan, a graduate student at the University of California at Berkeley, said Mr. Stark rejected a report by two professors, Stephen Walt and John Mearsheimer, who argued that the American government is in the thrall of pro-Israel zealots. The congressman noted that a professor popular on the left, Noam Chomsky of the Massachusetts Institute of Technology, also took issue with the paper, Mr. Bitzan said.

In a recent tally conducted by the Religion News Service, 393 House members described themselves as Christian or part of a denomination that considers itself Christian. Thirty said they were Jewish, two reported being Buddhists, and one was Muslim. On the opposite side of the Capitol, 87 senators reported being Christian, while 13 were Jewish.

The Sun contacted the six members of Congress found to be “unaffiliated” in that survey, Mark Udall of Colorado, Neil Abercrombie of Hawaii, John Olver and John Tierney of Massachusetts, Earl Blumenauer of Oregon, and Tammy Baldwin of Wisconsin. All are Democrats.

A spokeswoman for Mr. Olver, Sara Burch, said her boss did not wish to expand on the unaffiliated designation. “He just thinks religion is a personal matter,” she said. “‘Non-affiliated,’ that’s just his way of saying, ‘To me, it’s personal.'”

A spokeswoman for Mr. Blumenauer, Erin Allweiss, said the Oregon native had no comment. Ms. Baldwin and Messrs. Udall, Abercrombie, and Tierney did not respond to the Sun’s inquiry about whether their unaffiliated status should be viewed as a lack of religious belief.

A spokesman for the American Humanist Association, Fred Edwords, said the meager results of the contest undercut claims that secularists have taken over American society. “When people say there’s a war on Christianity or there’s a war on Christmas, they’re talking through their hats,” he said. Mr. Edwords said he regularly sees claims that atheists are dominating Congress, the bureaucracy, public schools, universities, and the courts. “The few of us that exist would be spread pretty thin if we’re supposed to be overrepresented in so many places,” he said.