A federal judge says the Food and Drug Administration overstepped its authority in efforts to regulate electronic cigarettes. Regulators began halting shipments of electronic cigarettes last year. The F.D.A. said it found cancer-causing ingredients in the products, despite manufacturers’ claims that they are safer than tobacco cigarettes. The agency argued that electronic cigarettes, which use a battery-operated vaporizer to produce a nicotine mist, are a combination drug-device, and therefore subject to stricter safety standards than cigarettes. But Judge Richard Leon of Federal District Court agreed with manufacturers that electronic cigarettes are “the functional equivalent of traditional cigarettes.”