The FBI is examining how American Home Products Corp. won approval to sell its diet drug Redux, which was linked to heart damage and eventually pulled from the market, a federal law enforcement official said yesterday.

The official, who requested anonymity, gave no other details. The company said it was not aware of any probe, the FBI said it could not confirm or deny an investigation was underway, and the Food and Drug Administration had no comment. The FBI conducts preliminary probes to determine whether to launch a formal investigation of possible criminal wrongdoing.

Shares of American Home Products were down 3 points at 39 1/2 in afternoon trading on the New York Stock Exchange. It was the second-most active issue and among the day's biggest losers.

The Wall Street Journal reported that the FBI was trying to find out whether American Home Products told the Food and Drug Administration everything it knew about adverse reactions to the diet pills.

The FDA approved Redux in 1996, but in 1997 AHP withdrew it and another diet drug, Pondimin, from the market after both were linked to heart valve damage.

American Home Products said it was not aware of any investigation of how it handled Redux or Pondimin, one-half of the "fen-phen" cocktail that has spurred thousands of lawsuits.

"American Home Products is absolutely unaware of any investigation by the U.S. Department of Justice or the Federal Bureau of Investigation relating to diet drugs," said AHP's general counsel, Louis Hoynes.

Hoynes added, "We know of no basis for such an investigation, and we are confident that American Home Products' actions with respect to Pondimin and Redux were at all times lawful and appropriate."

More than 4,000 suits have been filed by patients who say they were harmed by Pondimin or Redux. Last month, a Texas jury awarded one woman who took fen-phen $23.3 million in damages. The company also has settled suits with more than 36,000 women who used its Norplant contraceptive.