Support for a statewide water fluoridation mandate appears to be weakening on Beacon Hill, where the measure’s proponents say they want to study reports linking fluoride to health problems before taking a vote.

Sen. Pamela Resor, D-Acton, filed legislation to mandate fluoridation but now says research linking fluoridated water to bone cancer and other problems convinced her that lawmakers should perform a study before voting up or down on the bill.

“Certainly there are questions in my mind at this point,” Resor said. “There are strong dental health reasons for using fluoride. At the same time, there are these questions about some of the reports” on fluoride’s health effects.

Though Resor is the bill’s main sponsor in the Senate, she said she now does not have a position for or against the proposed mandate.

The bill’s , which Resor said was provided to her by advocacy group Health Care For All, would require fluoridation of any municipal water supply that serves at least 5,000 people.

Resor now wants to speak further with some of the legislation’s proponents, including the Boston University and Harvard dental schools, Blue Cross Blue Shield and the Massachusetts Medical Society.

“I plan to contact those groups who have sponsored and promoted this and see if any of these studies (suggesting negative health effects) are reliable,” Resor said.

Rep. Kathleen Teahan, D-Whitman, who filed identical legislation in the House, said she thinks research on fluoride’s negative health effects is “hypothetical.” But Teahan also wants lawmakers to study the matter further before deciding whether to require cities and towns to add fluoride to water.

“I think it’s always wise to take more time and get everybody’s viewpoints and that way you move forward with the best legislation,” she said.

Residents in more than one-third of Massachusetts communities drink fluoridated water largely because fluoridation is supported by many dental groups and the U.S. Centers for Disease Control and Prevention.

The American Dental Association says research shows fluoridation lowers tooth decay rates by 20 percent to 40 percent.

But a number of prominent scientists oppose fluoridation because of studies linking it to bone cancer in young boys, increased levels of lead in drinking water and hip fractures in women.

Water fluoridation’s opponents include Dr. Arvid Carlsson, winner of the 2000 Nobel prize in medicine, and 11 unions that represent 7,000 environmental and public health professionals at the U.S. Environmental Protection Agency.

On Beacon Hill, some lawmakers oppose mandating fluoridation because of concerns about health problems and a sense that cities and towns should be allowed to make the decision on their own.

Opponents of the mandate include Reps. Susan Pope, R-Wayland; David Linsky, D-Natick; and Sens. Karen Spilka, D-Ashland and Harriette Chandler, D-Worcester.

“Years ago, I think people believed fluoride had so many more positives and they weren’t aware there were potential negatives,” Spilka said. “All the research and medical evidence, it’s not as clear as it used to be, I believe.”

Linsky noted that fluoridation has been controversial in Natick, where the town began using the chemical despite unanimous opposition from an expert panel formed by town officials in 1997. Linsky said he doubts the Legislature will decide to mandate fluoridation statewide.

“I don’t think it’s a high priority of very many legislators,” Linsky said.

The proposal is pending before two Legislative panels: the committees on Public Health, and Children and Families.

Spilka, co-chairwoman of the Children and Families committee, said she doesn’t expect the panel to give the bill a favorable report.

“My gut is that it will not pass,” she said.

Rep. Peter Koutoujian, D-Waltham, co-chairman of the Public Health panel, said he expects the committee to debate the bill early in 2006 but doesn’t know how it will turn out. The committee heard from both sides of the controversy in a public hearing in October.

“We’re still considering this,” Koutoujian said. “The data that the fluoride has not been harmful has been prolific and mature. So as we consider some of these other studies being presented to us we just have to make sure we’re balancing them properly.”

While the Legislature may ask for a study on the bill’s merits before acting on it, it’s unclear who would perform the research. Linsky said he doesn’t know what agency “would have credibility with both sides of the issue.”

The National Research Council, a federal body that declared fluoridated water safe in 1993, is scheduled to issue an updated review of research in February.

A member of the Public Health committee, Rep. Deborah Blumer, D-Framingham, suggested waiting for the updated report before proceeding on the state proposal.

Blumer called herself a supporter of fluoridated water but said she’s concerned about research that suggests the most commonly used type of fluoride causes extra lead to escape pipes and get into the water supply.

“I’d really want to look at the new studies,” Blumer said. “I think it’s an area where we have the time to be cautious.”

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