Congress may soon join the skirmish between the Food & Drug Administration and the makers of dietary supplements. Although the industry claims the agency is trying to deny consumers access to vitamins and herbal products, the FDA says its policy is in limbo. "Our strategy is not to increase enforcement," says an official. "We want Congress to draw the lines" on an industry crackdown. Indeed, Representative Henry A. Waxman (D-Calif.) and Senator Edward M. Kennedy (D-Mass.) are considering legislation that would codify oversight of an industry that's largely ignored by regulators. They may require that supplements be safe but not demand the proof of effectiveness required for drugs. But makers would only be able to make claims backed by scientific evidence, ruling out many of the wilder assertions now made by manufacturers.