Federal regulators and antismoking groups are taking steps that could snuff out electronic cigarettes, the smokeless nicotine products embraced by a growing number of people trying to kick the habit or avoid bans on smoking in public.

Electronic cigarettes typically consist of a metal tube containing an atomizer, a battery and a cartridge filled with liquid nicotine. When a user sucks on an e-cigarette, a light-emitting diode causes the tip to glow and the atomizer turns the liquid nicotine into a vapor -- thus it is called...