The small Western Massachusetts towns of South Hadley, Granby, and Ludlow have been like peas in a pod for as long as anyone there can remember. So it was a surprise to South Hadley officials when the other two towns rejected a push earlier this year to add tooth decay-fighting fluoride to their shared water supply.

”We’re totally puzzled and dismayed,” said Fred Kowal, South Hadley’s public health director.

Kowal was particularly surprised when opponents from the towns came armed with studies from China that showed fluoride supposedly lowers the IQ of children and letters that seemed to indicate that scientists at the Environmental Protection Agency were against fluoridation.

It was another small victory in an increasingly heated war: A small and quirky assortment of scientists and activists from around the world has been remarkably successful in fighting the tide of fluoridation. Armed with obscure, footnote-laden studies and linked by the Internet, this core group has fueled scores of successful grass-roots campaigns that fly in the face of the entire public health establishment.

In Massachusetts alone, four towns, including Wilmington and Braintree, have rejected fluoride this year, while North Attleboro voted in June to fluoridate, but only after a messy debate. Water bills in Brewster this month will contain a question: To fluoridate or not?

Perhaps most prominent of the anti-fluoride braintrust is a cadre of outspoken scientists who work for the EPA, which regulates the country’s drinking water. The agency itself is strongly in favor of fluoridation. But this group has waged an intense internal war to change the policy and has taken its war public.

”We’re driving the pro-fluoride people nuts. … Here is a bunch of scientists within the agency that regulates drinking water saying drinking water is unsafe. That carries cachet,” said the leader of the dissident group, J. William Hirzey, a vice president of one of the agency’s employee unions.

In fact, the fluoridation debate rankles dentists in much the same way that scientists balk at debating the merits of creationism. They note that less than half the communities in Massachusetts have fluoridated water. The state ranks 35th in this regard. A report released this summer by the US surgeon general’s office said the lack of fluoridation in some areas is a public health travesty, resulting in untold cavities that could have been prevented.

But the Internet has placed the collective wisdom of their zealous opponents, who once worked in isolation, at the fingertips of any concerned citizen.

”I think local folks just get scared about fluoride and then are exploited by this traveling road show,” said Michael Easley, an associate professor of oral biology at the State University of New York Buffalo campus, who has made a second career of tracking the movement. ”The same so-called experts seem to turn up in all these places.”

Local officials who have opposed fluoridation say the EPA scientists give their cause a certain credibility.

”My biggest concern is that the EPA union was against fluoridation. If the actual researchers from the EPA, who are in charge of the policy, are questioning it, that really concerns me,” said Gregory Erickson, Wilmington’s public health director, who successfully encouraged his town’s health board to vote fluoridation down.

It is almost undisputed that the average American’s dental health has improved greatly in the past century. Water fluoridation is estimated to have cut tooth decay levels between 20 percent and 40 percent, according to the American Dental Association. Public health officials consider it safe and cheap: It costs each person about 52 cents a year in taxes.

About half of all Americans drink fluoridated tap water. Most of the Boston area’s water supply is fluoridated. Of the 289 communities in Massachusetts that have public water supplies, 121 are fluoridated. But 168 communities are not, and these tend to be in rural areas or far suburbs.

State law allows any community board of health to impose fluoridation. But residents can challenge it by collecting a certain number of signatures on a petition. That would put the issue to a vote. In Braintree, residents voted down fluoridation.

Public health boards can also just vote not to fluoridate, as was the case in Wilmington.

In South Hadley, officials are preparing to put the question on the ballot next spring. Residents of all three towns sharing the water supply would vote on it. But health board members in Granby and Ludlow are skeptical.

”Certainly if you look at some of the literature you see that fluoride is not totally without issues,” said Richard Bombardier, Granby’s health board chairman.

One of the places with such literature is the Web site for the Journal of the International Society for Fluoride Research. It has all the trappings of a mainstream academic journal, from the fonts used in the table of contents to the heavily footnoted papers produced by academics around the world. It was once run from the home of a Polish scientist, but is now based in the house of Kansas researcher. It’s unclear if it adheres to the same rigorous peer-review standards as most scientific journals.

Anti-fluoridationists believe fluoride might be responsible for cancer, birth defects, low IQs, and fragile bones. They also note that it causes fluorosis, or tooth staining, in a small number of people. Most dentists say this causes no discernible health problems.

And the anti-fluoridationists also have a more pragmatic argument: Since most people get fluoride from toothpaste and bottled drinks that use water from urban areas, why force smaller communities to fluoridate if they have health concerns?

On the numerous Web sites filled with material supporting these positions, the same collection of names surface repeatedly. One of those is Paul Connett, a chemistry professor at St. Lawrence University in New York.

”The Internet has been especially important, because the powers that be have suppressed all dissent. The ADA says there is no debate,” he said. ”The Internet puts us all on the same page. One community’s victory can help another community’s fight.”

Connett notes that much of Europe, except Ireland, does not fluoridate water supplies. He believes a domino effect of fluoridation defeats will soon topple the United States’s practice.

”I think Ireland is going to crack. Once that happens, England will not do anything. Canada will soon crack. Then the US will be isolated. It will become clear that this is an American thing,” Connett said.

The words and manifestos of Connett and his allies can, through the Internet, quickly end up in the hands of local activists, a synergy perhaps most dramatically illustrated in Natick. There, in 1997, a group of anti-fluoridation officials gathered many of these papers into one massive report, ”Should Natick Fluoridate?” or, as it is known among reverent anti-fluoridationists, the Natick Report.

”There are some citizens who are just misinformed, but then there is a small group of these hard-core activists around the country who just don’t care what the facts are,” said Myron Allukian, the Boston Health Commission’s director of oral health, who went to Natick to rebut the Natick Report. ”You just can’t change their mind.”

Allukian and his allies won, and today Natick residents drink fluoridated water, but the Natick Report has resurfaced in small-town debates around the country.

During the Wilmington fight, Erickson, the town’s health director, put his own anti-fluoridation thoughts on paper for the health board to consider. But months later, he was getting calls from activists as far away as California, asking for help in their local fights.

”Somehow my paper got on the Internet, ” Erickson said.

Allukian was one of the central figures in the drive to fluoridate Greater Boston’s water in the 1960s and ’70s. Many people opposed it then on the grounds that it smelled of state control and communism: the dental establishment forcing the public to drink medicated water.

When the Cold War cooled in the early 1990s, Allukian, a longtime dental health specialist, said he noticed a definite downturn in anti-fluoridation activity. That is, until the rise of the Internet.

”They really seem to be gearing up again,” he said.