NEW YORK — A federal judge has struck down a law that restricted the information drug companies could give doctors about unapproved uses of medicines.

U.S. District Judge Royce Lamberth ruled yesterday that government arguments supporting the Food and Drug Modernization Act were "preposterous."

"This is a major victory for drug companies," said Hemant Shah, an analyst with HKS & Co. in Warren, N.J.

At issue was the distribution of research reports and medical journal articles on using drugs for illnesses other than the ones they were originally approved for by the government.

The Food and Drug Administration had sought to restrict drug companies from promoting their products by distributing the reports or holding seminars about the studies, contending that the companies might stress only the benefits of their products and not balance that with any reports or problems.

The FDA argued that its rules do not violate free speech because they allow the companies to distribute the materials under certain conditions, such as disclosing any relationship between the company and researcher, listing other products for the illness in question and providing a list of other articles on the drug.

Lamberth ridiculed that argument, saying that "the First Amendment is premised upon the idea that people do not need the government's permission to engage in truthful, non-misleading speech about a lawful activity."

Under his ruling, the studies the companies provide to doctors cannot be false or misleading, and drug company salesmen must disclose any association between the company and researcher.

The company also must disclose whether the treatments detailed in the studies have been approved by the FDA.

Peggy Dotzel, FDA acting associate commissioner for policy, said the agency was studying the ruling to prepare a response.

"It would appear the judge's ruling is consistent with the constitutional protection of the right to commercial speech," said Jeff Trewhitt, a spokesman for the Pharmaceutical Research and Manufacturers of America, which represents drug companies. "The judge has outlined a workable approach."

The drug industry will still have an incentive to seek FDA approval for new uses for already approved drugs because it will be necessary for any advertising claims, Trewhitt said.

Last week, a federal judge ordered Eli Lilly & Co. to stop promoting its osteoporosis drug Evista as a breast-cancer prevention drug. The company has done studies on Evista's use in preventing breast cancer, but that use has not been FDA-approved.

Shawn Gunnarson of the Washington Legal Foundation, a conservative group that had challenged the law, was pleased with the ruling: "It makes it very clear that the First Amendment is alive and well."