Federal investigators and Harvard University officials are probing whether a Harvard professor buried research suggesting a link between fluoridated tap water and bone cancer in adolescent boys.

The National Institute of Environmental Health Sciences (NIEHS), which funded Chester Douglass's $1.3 million study, and the university are investigating why the Harvard School of Dental Medicine epidemiologist told federal officials he found no significant correlation between fluoridated water and osteosarcoma, a rare form of bone cancer. Douglass, who serves as editor in chief for the industry-funded Colgate Oral Care Report, supervised research for a 2001 doctoral thesis that concluded boys exposed to fluoridated water at a young age were more likely to get the cancer.

The Environmental Working Group, an advocacy organization, urged federal officials late last month to explore whether Douglass had skewed his 2004 report to the institute to play down possible risks associated with fluoridation.

The practice of fluoridating tap water -- which more than 170 million Americans drink -- has inspired controversy for years, but the majority of federal and state officials back it as a highly effective way to prevent tooth decay. The Centers for Disease Control and Prevention has ranked fluoridation as one of the top 10 health achievements of the 20th century, and numerous studies have shown that fluoridation prevents tooth decay. The National Cancer Institute states on its Web site: "Many studies, in both humans and animals, have shown no association between fluoridated water and risk for cancer."

Douglass reported last year that the odds of having osteosarcoma after drinking fluoridated water was "not statistically different" from the risk after drinking non-fluoridated water. But in 2001, Douglass's doctoral student, Elise Bassin, published a thesis using his data that concluded: "Among males, exposure to fluoride at or above the target level was associated with an increased risk of developing osteosarcoma. The association was most apparent between ages 5-10, with a peak at six to eight years of age."

Bassin's thesis work is considered the most rigorous human study to date on a possible connection between fluoridation and osteosarcoma, a rare but lethal form of cancer that affects males nearly twice as often as females. Patients with the cancer live an average of three years after diagnosis. In 1990, an animal study by the National Toxicology Program found "equivocal evidence" of a link between fluoridated water and cancer in male rats. And more than a decade ago, a New Jersey Department of Health survey found that young males in fluoridated communities had a higher rate of osteosarcoma than those in non-fluoridated communities.

"Fluoride safety is a major public health issue, and a Harvard professor potentially falsifying public research results has huge public health implications," said Richard Wiles, senior vice president of the Environmental Working Group. He added that Douglass's role in editing a newsletter funded by Colgate-Palmolive Co. "creates the appearance of a conflict of interest."

Douglass, who has taught at Harvard since 1978 and has edited the Colgate quarterly since 1997, referred inquires to the university's press office. Harvard Medical School spokesman John Lacey said the school "takes all allegations of misconduct seriously and has a standard system for reviewing allegations of research impropriety. The school is assembling an inquiry committee to review the questions raised concerning the reporting of this work."

Douglass has not edited for the newsletter articles on the possible connection between fluoridation and cancer and has not testified publicly on the issue, Lacey added.

The institute issued a statement similar to Harvard's, saying the NIEHS "takes allegations of misconduct very seriously" and is reviewing the matter.

Bassin could not be reached.

Some public health experts, including Richard Clapp, an expert in the environmental causes of cancer at Boston University's School of Public Health, think Bassin's study should prompt additional research. Researchers suspect a possible connection because half of ingested fluoride is deposited in bones, and fluoride stimulates growth in the end of bones, where osteosarcoma occurs. The Environmental Protection Agency has commissioned a National Academy of Sciences study to examine the safety of fluoridation. A report is due next year.

"It's important, and it needs to be followed up," Clapp said of Bassin's work. "There's a legitimate biological rationale for focusing on young boys."