LONDON, Oct. 21 -- British atheists announced Tuesday a high-profile advertising campaign to put posters on London buses that say: "There is probably no God. Now stop worrying and enjoy your life."

By Tuesday night, as many as 3,400 donors had given about $80,000 on a Web site set up to take contributions to fund the ads. The money arrived along with messages that ranged from witty to nasty, summed up by one from a donor who gave 25 pounds ($42): "Hoorah for the non-believers!"

"We wanted it to be a positive message," said Hanne Stinson, chief executive of the British Humanist Association, which plans to advertise on buses starting in January. "It's about telling people that it's okay if you don't believe in God. If it raises a smile, too, good."

While the vast majority of Britons identify themselves as Christians, only a small percentage attend services regularly. Atheism is far more popular, and socially and politically accepted, in Britain than in the United States.

Many people who do not believe in God call themselves humanists or secularists. The British Parliament has an active and growing group of legislators who describe themselves as humanists.

One of the world's most outspoken and provocative advocates of atheism, Oxford University Prof. Richard Dawkins, best-selling author of "The God Delusion," is a member of the humanist association and pledged to personally match donations up to 5,500 pounds (about $9,300), Stinson said.

"This campaign to put alternative slogans on London buses will make people think -- and thinking is anathema to religion," Dawkins is quoted as saying on the Web site.

The Church of England issued a statement Tuesday defending the humanists' right to express their views but disagreeing with their message. "Christian belief is not about worrying or not enjoying life," it said. "Quite the opposite: our faith liberates us to put this life into a proper perspective. Seven in ten people in this country describe themselves as Christian and know the joy that faith can bring."

In an interview, Stinson said the initial goal was to raise 5,500 pounds, enough to put advertising on the sides of 30 of London's extra-long "bendy buses" for four weeks. But the Web site was swamped with donors.

One person pledged 10 pounds and left the comment, "Spread the word, and consign this superstitious nonsense to the dustbin of history! America, are you listening?"

Another donated 5 pounds and said, "Marvelous. Sorry it's just a fiver -- I'm between jobs at the moment."

Stinson said she was surprised by the outpouring: "It says something about the very loud voice that religion has in our society. People want something to balance that off." The campaign's unexpected success could mean it will be expanded to include posters inside buses or in the London subway.

A spokesman for Transport for London, which operates city buses, said buses have carried ads for religious groups, but never ads promoting atheism. He said the humanists had not yet formally submitted an ad request.

The ads are "not intended as an attack" on anyone's faith, Stinson said. In her view, they do not encourage people to become atheists, but rather are meant to offer support to "people who already do not believe in God."

The idea for an atheist ad campaign first surfaced in June, as a suggestion by television comedy writer and journalist Ariane Sherine in a column in the online version of the Guardian newspaper. Sherine noted that ads running on the London buses at the time directed people to a Web site that declared that those who do not believe in God will spend "all eternity in torment in hell."

The humanist association agreed to take on the project. The bus ads are designed to tell atheists that they will not burn forever in the "lake of fire" described on the religious Web site, Stinson said. "It's about reassurance."