With the Food and Drug Administration set to hold hearings next week on the safety of popular painkillers like Bextra and Celebrex, a U.S. Senator is charging that the agency is preventing one of its scientists from presenting results from the largest and most recent study of heart risks posed by the drugs.

The study, which was co-written by FDA scientist David Graham, a longtime critic of the medications that belong to a class of drugs called cox-2 inhibitors, is based on a large California Medicaid database to reveal heart risks posed by a wide range of painkillers. Cox-2 drugs include Bextra, Celebrex and Vioxx, the Boston Globe reported Saturday.

This would mark the third time in recent months that the FDA had been accused by Congress of ignoring research by its own scientists. In each case, the research was later confirmed by other scientists, the newspaper said.

In a letter to the FDA, Sen. Charles Grassley, an Iowa Republican, asked why the agency failed to make a review of the California study a priority, ‘‘given the urgent regulatory and drug safety issues.”

The letter, sent Friday night to FDA acting commissioner Lester Crawford, demanded a formal reply no later than Wednesday, the day the FDA hearings are scheduled to begin, the newspaper said.

The FDA did not immediately respond to requests for comment, the Globe said.

The hearings were prompted by Merck & Co.‘s decision last September to pull Vioxx from the market after research showed long-term use of the drug increased the risk of heart attack and stoke.

Although originally introduced as a better alternative to traditional nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen and naproxen - all of which increase the risk of gastrointestinal bleeding - recent evidence suggests that cox-2s may elevate the risk of heart attack and stroke.