BERKELEY, Calif. – For an atheist, Maxim Schrogin talks about God a lot.

Over lunch at a Jewish deli, he ponders the impulse to believe — does it come from within or without? Why does God permit suffering? Finally, he pulls out a flowchart he made showing degrees of belief, which ranges from unquestioning faith to absolute atheism. He stabs the paper with his pen.

"This is where I fall," he said. "Zero."

Still, Schrogin, 64, is a dues-paying member of Congregation Beth El, a Reform synagogue here in Berkeley. He is among its most active members, attending Torah study, and, for a time, heading its social action committee. He organizes its community service projects and works with leaders of other congregations to help the poor.

His two children were bar and bat mitzvahed. On Friday nights, he and his wife light Shabbat candles and recite Hebrew prayers. There is one song, sung by the congregation in Hebrew, that can bring him to tears.

Schrogin isn't alone.

At the High Holy Days of Rosh Hashanah and Yom Kippur, many Jews who identify as atheists, secular humanists and other religious "nones" attend synagogue. Most go once a year — like Christians who go to church only at Christmas or Easter. But others, like Schrogin, are active, integral parts of a religious community that, ideologically, they stand apart from.

"Atheism and Judaism are not contradictory, so to have an atheist in a Jewish congregation isn't an issue or a challenge or a problem," Shrogin said. "It is par for the course. That is what Judaism is. It is our tradition to question God from top to bottom."

Atheism is entrenched in American Judaism. In researching their book American Grace, authors Robert Putnam and David Campbell found that half of all American Jews doubt God's existence. In other groups, that number is between 10 and 15 percent.

Those figures have some in the Jewish community alarmed. A recent issue of Moment, a magazine of Jewish thought, asked influential Jews if Judaism can survive without God. The answers were split.

"I'm not sure," Leora Batnitzky, a Princeton professor of religion, wrote in Moment. "The question comes down to what it means to sustain a belief in God in Judaism, and that's a complicated issue."

And one that Jews have been debating for centuries.

Unlike other religions, Judaism has often embraced its atheist strain. The 18th-century Dutch philosopher Baruch Spinoza was excommunicated from his Jewish community for equating God with nature. Today, his writings are studied by many Jews.

In the 1920s, American Conservative Rabbi Mordecai Kaplan developed the theology of what would become Reconstructionist Judaism, founded on the idea that God is not personal, but a summation of all natural processes. Four decades later, Reform Rabbi Sherwin Wine came out as an atheist and founded "Humanistic Judaism," which emphasizes secular Jewish culture and history over belief in God.

And because Judaism is not dogmatic — unlike Christianity and Islam, there is no creed to adhere to — atheists can be open about their lack of belief and still belong to a synagogue.

"Atheism is not much discussed in Jewish life," said Jonathan Sarna, a professor of American Jewish history at Brandeis University.

"An individual who attends synagogue, participates in Jewish communal affairs, and contributes heavily to Jewish charities would undoubtedly be considered a very fine Jew, without asking questions about whether or not that person believed in God."

Which means rabbis and their congregations welcome the doubter.

"The atheist challenges knee-jerk faith," said Rabbi Naomi Levy of Nashuva congregation in Los Angeles. "I love when the atheist asks, 'What's the point of prayer?' or, 'Why are you following these rituals?' These questions cause us to think, to give thoughtful responses, to reassess our own beliefs and convictions."

Shaul Magid, a professor of modern Judaism at Indiana University, said atheists may join synagogues because American Judaism lacks "a vibrant secular Jewish movement."

"They go because they want some kind of ethnic identity," Magid said. "They don't care about the prayers. It allows them to feel a sense of Jewishness, but has little to do with religion."

That's what prompted Jennifer Cohen Oko, a Washington, D.C.-based writer, to join a Reform synagogue, her first. Neither Cohen nor her husband believe in God, but, like many Jews, they joined for their two children.

"I want my kids to understand they are Jewish, to be proud of being Jewish and to understand their heritage," Cohen said. "And then they'll have a choice. If they want to go that way (towards belief in God), great. If they don't, they'll have a sense of where they came from."

Children are what brought Schrogin to Beth El, but he has stayed for the sense of purpose organizing its community service projects has instilled.

"My rabbi said, 'You know Maxim, God doesn't care whether you believe in him or not. All that he cares is that you do the right thing.' Our action in the world is much more important."