The Food and Drug Administration said Tuesday that it had discovered the toxic chemical melamine in infant formula made by an American manufacturer, raising the possibility that the problem was more extensive in the United States than previously thought.

While few details were available late Tuesday, agency officials said they had discovered melamine at trace levels in a single sample of infant formula. It was also discovered in several samples of dietary supplements that are made by some of the same manufacturers who make formula.

F.D.A. officials insisted that the levels of melamine were so low that they did not pose a health threat.

“There’s no cause for concern or no risk from these levels,” said Judy Leon, an agency spokeswoman. Ms. Leon said the contamination was most likely the result of food contact with something like a can liner, or from some other manufacturing problems, but not from deliberate adulteration.