WASHINGTON (AP) — Federal regulators on Tuesday defended their assessment that a chemical widely used in plastic baby bottles and in food packaging is safe, even as a preliminary study reported that it was associated with increased risks for heart disease and diabetes.

“A margin of safety exists that is adequate to protect consumers, including infants and children, at the current levels of exposure,” Laura Tarantino, a senior Food and Drug Administration scientist, told an expert panel that has been asked for a second opinion on the agency’s assessment of bisphenol A, or BPA.

The new study, released Tuesday by The Journal of the American Medical Association, was based on a survey of nearly 1,500 adults. It found that those with higher levels of BPA in their urine were also more likely to report that they also had heart disease or diabetes. But the investigators wrote that their approach “may have resulted in false-positive associations” and urge that the study be independently replicated.

Two Dartmouth College analysts of medical research said the study, which does not prove that BPA caused the health problems, raised questions but provided no answers about whether the ubiquitous chemical is harmful.

Dr. Lisa Schwartz and Dr. Steven Woloshin of the Dartmouth Institute for Health Policy and Clinical Practice said the study presented no clear information about what might have caused participants’ heart disease and diabetes. The study did not look at exposure to BPA, but only at levels measured in a single urine test. “Measuring who has disease and high BPA levels at a single point in time cannot tell you which comes first,” Dr. Schwartz said.

The researchers did a broad search for diseases that might show an association, generally providing weaker evidence. In particular, there was no prior reason to suspect that heart disease might be linked to BPA. They used statistical modeling of the health survey population to make their comparisons. For example, fatter people had higher levels of the compound, and the researchers tried to correct for that with statistics.

“We recognize the need to resolve the concerning questions that have been raised,” Ms. Tarantino said. The agency said that the studies with rats and mice that it relied on for its assessment were more thorough than some of the human research that had raised doubts.

The journal article was released to coincide with the agency’s scientific advisers’ hearing.

BPA is used in hardened plastics in a wide range of consumer goods including eyeglass lenses and compact discs. The F.D.A. has the authority to limit the use of BPA in food containers and medical devices but last month released an internal report concluding that BPA exposure did not warrant action.

In the study released Tuesday, researchers from Britain and the University of Iowa examined a United States government health survey of 1,455 American adults who gave urine samples in 2003-04 and reported whether they had any of several common diseases. Participants were divided into four groups based on BPA urine amounts; more than 90 percent had detectable BPA in their urine.

A total of 79 reported that they had had heart attacks, chest pain or other types of cardiovascular disease, and 136 reported that they had diabetes. After the statistical modeling, the investigators reported that higher BPA levels were associated with a greater risk of having heart disease or diabetes. They found no connection between BPA and other ailments, including cancer.