The Gatwick Area Conservation Campaign has published a document suggesting that a new runway at Stansted or a new airport at Cliffe in north Kent would be preferable in terms of noise, air pollution and economic impact.
Fellow anti-runway groups said they regretted the move, which breaks an informal agreement among airport communities not to point the finger at each other.
Residents around Heathrow, Gatwick, Stansted and Cliffe have spent the last year fighting plans for airport development, meeting regularly to coordinate their campaigns.
In its submission to the transport secretary Alistair Darling's consultation on airport expansion, the Gatwick group said that the most modest expansion proposal, a close parallel runway, would expose 3,800 people to nitrogen pollution above European limits, compared with 20 at Stansted and none at Cliffe.
A wide-spaced runway would leave 52,000 people around Gatwick suffering unacceptable noise pollution -twice as many as an equivalent development at Stansted, and four times the number at Cliffe. The economic benefits would be lower than at either of the other sites, according to the submission.
Brendon Sewill, who chairs the Gatwick group, pointed out that the airport was in the consultation only because legal action by local authorities in Essex and Kent had forced the government to include it. Mr Sewill said: "We've been the strongest supporters of the consensus that there should be no new runways anywhere.
"But we were deeply disappointed when Stansted and Cliffe broke that consensus by seeking a judicial review which landed us in this situation. People here are basically extremely cross about it."
The Gatwick campaign said its preferred option was still no expansion anywhere, or an offshore site miles from housing. But Mr Sewill said if there were new runways, the Sussex airport was particularly unsuitable because of the "constricted nature" of the site, surrounded by hills, towns and villages.
Jeff Gazzard, the coordinator of the environmental group AirportWatch, described the submission as "churlish", saying: "Nimbyism has no place in this argument. Shifting things around is no good for anybody."
The pro-runways pressure group Freedom to Fly, which is supported by airlines, transport unions and business chiefs, leaped on the dispute, saying the environmentalists' alliance was falling apart.
Dan Hodges, Freedom to Fly's director, said: "Civil war is effectively breaking out among the opponents of airport expansion. Sadly, this is what occurs when national campaigns such as Friends of the Earth and AirportWatch start to play politics with local issues."
The government's consultation on runways began last summer. It was restarted in February after a high court judge ordered Mr Darling to add Gatwick to the options.
Paul de Zylva, an aviation campaigner for Friends of the Earth, said communities had stuck together until now despite "intolerable pressure".
He added: "Freedom to Fly can hardly say their members are unanimous in the aviation industry - they're constantly bickering."
