In a decision with potentially far-reaching implications for how doctors prescribe drugs, a federal judge ruled yesterday that the Food and Drug Administration cannot stop the pharmaceutical industry from encouraging physicians to use medications for unapproved purposes.

The ruling will further curb the FDA's already limited ability to control so-called off-label use of medications and allow companies to conduct seminars for physicians and distribute information to them about a drug as long as the FDA has approved it for some purpose.

Doctors are already allowed to prescribe any drug for use once it has been approved by the FDA for some use. The new ruling means that drug companies will be freer to more aggressively promote this practice, which can yield both spectacular benefits and catastrophic tragedies.

On July 20, for example, the New England Journal of Medicine rushed into publication a report that spironolactone, a drug used for 40 years in the treatment of water retention, cut death rates dramatically as an "off-label" treatment for congestive heart failure.

But Georgetown University pharmacology chief Raymond Woosley noted that powerful drugs designed to treat severe heart rhythm irregularities were still being prescribed off-label for "trivial arrhythmia" even after they had caused 50,000 deaths by some estimates. Sales of one of these drugs were stopped in 1989, but another one, Tambacor, is still on the market.

U.S. District Judge Royce C. Lamberth's memorandum yesterday ruled unconstitutional portions of last year's Food and Drug Administration Modernization Act that regulate the pharmaceutical industry's ability to distribute information on off-label drug applications.

"The government, however benign its motivations, simply cannot justify a restriction of truthful, nonmisleading speech on the paternalistic assumption that such restriction is necessary to protect the listener from ignorantly or inadvertently misusing the information," Lamberth wrote.

Jeff Trewhitt, spokesman for the Pharmaceutical Research and Manufacturers of America, said that the drug companies were "reviewing this decision," and "it would appear the judge's ruling is consistent with the constitutional protection of commercial speech."

The FDA also limited itself to a brief comment: "We'll have to carefully evaluate the decision and determine what we have to do as a follow-up," said Peggy Dotzel, the FDA's acting associate commissioner for policy.

But Dan Troy, one of the lawyers for the Washington Legal Foundation, plaintiffs in the case against the FDA, called Lamberth's ruling "total vindication of our position." He said he expected the FDA to appeal.

The foundation, a free-market advocacy group that Troy said does not represent the pharmaceutical industry, filed suit against the FDA in 1994 over the agency's guidelines on promotion of off-label drug uses.

In a summary judgment one year ago, Lamberth found the FDA's guidelines unconstitutional. But after passage of the FDA Modernization Act, Lamberth agreed to review his ruling.

The redrawn guidelines contained in the law allowed pharmaceutical companies to disseminate peer-reviewed journal articles and texts to doctors as long as the firm met a list of conditions.

The law included a provision requiring the manufacturer to apply to the FDA for a new application for a drug before promoting it. Another provision required the manufacturer to submit promotional materials to the FDA for review before distribution. A third required the manufacturer to report semiannually on its promotional activities.

Lamberth rejected all of these requirements as indefensible violations of the Constitution: "The supplemental application requirement of the act amounts to a kind of constitutional blackmail," Lamberth wrote. "Comply with the statute or sacrifice your First Amendment rights."

The pharmaceutical companies' Trewhitt said that the industry interpreted Lamberth's finding narrowly -- confirming "the right of a company to give a reprint of a medical journal article to a doctor" as long as it is not "false or misleading" and as long as the company "discloses its interest in the drug" and notes that the application does not have FDA approval.

Still, Georgetown's Woosley explained that the problem for the FDA is that a drug company unfettered by government regulation is unlikely to disseminate information that does not support its cause.

"We see all the time that advertising and promotion of medications exceeds the bonds of scientific accuracy, and you have to address it one way or another," Woosley continued. "Physicians need to know about off-label applications, but they need balanced information, and there is no impartial arbiter" that can give it to them.

This has left the FDA with two bad options -- abandon the field to the industry, or try to restrict its access to physicians and risk the wrath of the Constitution. "We thought it was kind of silly," said one congressional source knowledgeable about the drafting of the FDA Modernization Act. "How do you tell doctors what to read?"