DAVIE, Florida — When South Florida atheists held their first meeting, they were just five friends, having a beer at a bar.

Four years later, they've moved to a bigger place -- still a bar -- to hold their weekly meet-and-greets. Membership is up to almost 500, Darwin Day is in the planning stages and bumper stickers are on sale.

"There is no God, but ice-cream is great," reads one. "What schools need is a moment of science," reads another.

Atheist groups are growing all over the United States, challenging stereotypes and confronting what they consider a big backslide in the separation of church and state.

They are chatting online, picking up trash along "adopted" highways, and advertising on buses and billboards. In South Florida, they recently picketed a prayer meeting in a public safety building paid for with tax dollars.

"We're growing by leaps and bounds," said Bob Senatore, a retired teacher and one of the early members of the Florida Atheists and Secular Humanists, or FLASH. "The attitude is, 'If we don't do something about it now, we'll be living under a theocracy.'"

Polls show non-believers are on the rise in the United States, even in places like Florida, where, as Senatore sees it, "There's a church on every corner and a fish on every car."

The fish is one of the most common symbols of Christianity.

The American Religious Identification Survey recently found the number of people who claimed "no religion" had nearly doubled nationally over the last 18 years, to 15 percent. They were the only demographic that increased in all 50 states.

Some attribute the surge to outrage over former president George W. Bush and his courting of the religious right. Others mention a slew of best-selling books about atheism that have recently fueled debate.

But there's no doubt the Internet is playing a role too. It offers atheist dating services, and helps nonbelievers meet up -- people who might otherwise remain "loners."

"To have a non-belief is not much to build a social group on," acknowledged FLASH member Jay Berman, a computer trainer and self-described Jewish atheist.

Berman said he wasn't looking to convert anyone to atheism, and takes a non-confrontational stance with religious friends.

"I'm happy to attend any religious observances where the food is good," he said.

For others, atheism is a cause. Along with freethinking and agnostic groups, they are beginning to lobby Congress on everything from stem cell research to civil rights.

The Secular Coalition for America represents 10 such organizations. Executive director Sean Faircloth said the coalition was particularly interested in bringing down state laws that give special privileges to religious-based services.

Groups like his took note when President Barack Obama nodded to "non-believers" during his inaugural speech.

"We've gone from where we essentially could communicate only with Congress, to now, where we have some open doors at the White House as well," Faircloth said. "I see tremendous progress and I feel real hope for the future, that you're going to hear more of us."

In fact, one of the biggest hurdles to political recognition for atheists may be their own free-thinking spirit.

"If a politician were to come out and say they were an atheist, I would be proud someone had the guts to do it," said Peter Ragona, a wedding photographer and member of FLASH. "But I would not vote for them just because they're an atheist."

According to the coalition, just one US lawmaker has gone on record as a "non-theist" -- California Democrat Peter Stark.

As they work to crack stereotypes, atheists are sometimes encountering resistance. Last month, when FLASH erected a billboard stating, "Being a good person doesn't require God," a local woman led children in chants calling for the sign to come down. Owners of a nearby beauty supply shop complained business was suffering.

In Iowa, the transit authority removed atheist ads from the sides of buses after complaints from riders. Authorities later put them back up, after talking to atheist organizers. When a Christian driver refused to drive a bus bearing the ad she was suspended.

FLASH president and firefighter Ken Loukinen said he regularly receives hate mail.

"I've had some threats to blow up my truck," said Loukinen, who is also state director of the national group American Atheists. But, he added, "We'd rather spread information than complain about stuff. We want to dispel myths about atheists, myths about science."

Taking a page from the playbook of the gay-rights movement, some atheists say "coming out" will drive up membership all by itself, as other atheists realize they are not alone.

"There are many people in misery, emotionally torn apart by their doubts. I've been there," said Ronelle Delmont, a book reviewer and former belly-dancer at the Davie meet-up. Delmont started studying science and atheism 15 years ago. Carl Sagan became her hero.

"I found courage by finding other people," she said. "I'm now unashamed to say I'm an atheist."