BETHESDA, Md. — The pharmaceutical industry mounted a new challenge on Friday to a federal plan that would require generic drug companies to take the initiative to update their labels to warn consumers whenever health risks were discovered, a shift that would expose the companies to legal liability.

During a public meeting at the Food and Drug Administration, the industry proposed instead that the F.D.A. itself should decide whether new warnings on drug labels are required and, if so, order companies to make the changes. But consumer advocacy groups said the companies were trying to shift responsibility to an agency that lacks the resources to track the vast array of drugs on the market.

More than 80 percent of prescriptions in the United States are now filled by generic versions of a drug, and most states permit pharmacists to dispense a generic in place of a prescribed brand-name drug. Millions of Americans take generics.

Under current rules, generic drug makers are not allowed to update such health warnings unless the F.D.A. orders them to do so — a peculiarity of the 1984 law that governs the generics. Brand-name producers make changes as they discover risks, and the F.D.A. approves them later, prompting changes in generic labels.