WASHINGTON — A judge today blocked a federal requirement that would have begun forcing tobacco companies next year to put graphic images on their cigarette packages to show the dangers of smoking.

U.S. District Judge Richard Leon ruled that it’s likely the cigarette makers will succeed in a lawsuit claiming the images violate the free speech amendment to the Constitution. He stopped the requirement until the lawsuit is resolved, which could take years.

Leon held a hearing on the case in September and questioned the Justice Department about whether the nine graphic images approved by the Food and Drug Administration in June convey just the facts about the health risks of smoking or go beyond that into advocacy — a critical distinction in a case over free speech.

The images include a cloud of cigarette smoke within inches of a baby’s face; a pair of healthy lungs next to the diseased lungs of a smoker and a warning that smoking causes fatal lung disease; a smoker’s stained teeth and a lip diseased by cigarettes; and a dead smoker on an autopsy table with surgical stitches in his chest and the words “Smoking can kill you.”

The FDA requirement said the labels were to cover the entire top half of cigarette packs, front and back and include a number for a stop-smoking hotline. The labels were to constitute 20 percent of cigarette advertising, and marketers were to rotate use of the images.

The Justice Department argued the images coupled with written warnings were designed to communicate the dangers to youngsters and adults. The FDA declined to comment on the judge’s ruling.

Tobacco companies are increasingly relying on their packaging to build brand loyalty and grab consumers. It’s one of few advertising levers left to them after the government curbed their presence in magazines, billboards and TV, and the graphic labels could cost them millions in lost sales and increased packaging costs.

The cigarette makers that sued the FDA are R.J. Reynolds Tobacco Co. of Winston-Salem, N.C., Lorillard Tobacco Co. of Greensboro, N.C., Commonwealth Brands Inc. of Bowling Green, Ky., Liggett Group of Mebane, N.C., and Santa Fe Natural Tobacco Co. of Santa Fe, N.M.