A federal judge yesterday told the Food and Drug Administration it must disclose thousands of pages of safety data on silicone gel breast implants, rejecting arguments from the agency and the implants' manufacturer that doing so would disclose crucial trade secrets to competing firms.

The ruling by U.S. District Judge Stanley Sporkin was a major victory for Public Citizen Health Research Group, which sued the FDA in 1988 under the Freedom of Information Act seeking access to studies that showed some implant materials caused cancer in rats.

Until now, the FDA has declined similar requests for data on other products, citing an exemption to the FOIA under which agencies do not have to release privileged commercial information obtained from private firms.

The FDA had argued in court that release would impair its ability to get safety information from other drug manufacturers, an argument that Public Citizen Health Research Group director Sidney Wolfe called "absurd."

"For the better part of the 19 years we've existed, we've attempted to crack through these trade secret exemptions to the FOIA at the level of the FDA," Wolfe said. "This is now the first time we've actually gotten the data."

FDA officials had no immediate comment. Robert Grupp, a spokesman for Dow Corning, the major implant manufacturer, declined comment on the ruling but defended the product, saying Dow has "hundreds of studies documenting its safety."

More than 2 million women in the United States have silicone implants, and the number of women seeking them -- most for cosmetic reasons -- is rapidly increasing, according to studies cited in yesterday's ruling. The implants, which consist of a closed, breast-shaped bag containing silicone gel, are also used for breast reconstruction after cancer surgery.

Yesterday's ruling dealt with two classes of information sought by Public Citizen: a file of consumer complaints kept by Dow Corning, and more than 750 animal studies, conducted by Dow or on the company's behalf, focusing on effects of implants in rats. The FDA did not oppose disclosure of the consumer complaint file, but Dow Corning objected to release of any of the information.

In his ruling, Sporkin sharply criticized the FDA for not releasing the animal studies voluntarily and dismissed its argument that disclosure would impede its data collection ability. "The FDA would have this court believe that it is the most impotent agency in Washington, and that the only way it can protect the public's health and welfare is by begging manufacturers of possibly lethal devices to submit information voluntarily," Sporkin wrote.

The agency is expected to issue regulations requiring additional safety studies by manufacturers next month.

Attorneys for the FDA had argued in court that because no such regulations existed yet, Dow was not required to turn over the studies, and that any information it did turn over should be treated as confidential. Sporkin rejected that argument as well.

"The {FDA} has done little, if anything, to implement this extremely important and necessary authority for over 13 years," he wrote. "To now use this delay as an excuse for continued ineffective regulation is nothing less than chutzpah being elevated to new heights."