WASHINGTON (Reuters) - A U.S. judge sided with tobacco companies on Wednesday, ruling that regulations requiring large graphic health warnings on cigarette packaging and advertising violate free-speech rights under the U.S. Constitution.

Cigarette makers challenged the U.S. Food and Drug Administration's rule requiring companies to label tobacco products with images of rotting teeth, diseased lungs and other images intended to illustrate the dangers of smoking.

"The government has failed to carry both its burden of demonstrating a compelling interest and its burden of demonstrating that the rule is narrowly tailored to achieve a constitutionally permissible form of compelled commercial speech," U.S. District Judge Richard Leon said.

While educating the public about the dangers of smoking "might be compelling, an interest in simply advocating that the public not purchase a legal product is not," Leon wrote in a 19-page ruling.

Further, Leon noted that the warning labels were too big to pass constitutional muster and that the government has numerous tools at its disposal to deter smoking such as hiking cigarette taxes or including simple factual information on the labels rather than gruesome images.

Congress in 2009 passed a law ordering the FDA to adopt the label regulation, which requires color warning labels big enough to cover the top 50 percent of a cigarette pack's front and back panels, and the top 20 percent of print advertisements.

Tobacco companies, including Reynolds American Inc's R.J. Reynolds unit, Lorillard Inc, Liggett Group LLC, Commonwealth Brands Inc, which is owned by Britain's Imperial Tobacco Group Plc, and Santa Fe Natural Tobacco Co Inc challenged the rule, arguing that it would force them to engage in anti-smoking advocacy against their own legal products.

"Unfortunately, because Congress did not consider the First Amendment implications of this legislation, it did not concern itself with how the regulations could be narrowly tailored to avoid unintentionally compelling commercial speech," Leon wrote.

The judge last year granted a preliminary injunction blocking the new label requirement from taking effect, a decision that the Obama administration has appealed.

A spokesman for the Justice Department, which represented the FDA in the case, had no comment.

The case is R.J. Reynolds Tobacco Co et al v. FDA, U.S. District Court for the District of Columbia, No. 11-1482.