WASHINGTON — A federal judge ruled yesterday that tobacco companies have violated civil racketeering laws, concluding that cigarette makers conspired for decades to deceive the public about the dangers of their product and ordering the companies to make landmark changes in the way cigarettes are marketed.

But U.S. District Judge Gladys Kessler said that under a 2005 appellate court ruling, she could not impose billions of dollars in penalties that had been sought by the Justice Department in its civil racketeering suit against the eight defendant tobacco companies.

All she could do, she said, was try to deter future illegal acts by the companies, and to that end, she ordered them to stop using terms such as "low tar," "light" and "mild" and to undertake a massive media campaign in an effort to correct years of misrepresentations.

It is a penalty that will cost the industry millions of dollars — a fraction of the cost of sanctions the companies faced at the outset of the case, when the Justice Department sought $280 billion from the industry.

In the opinion, Kessler wrote that there is "overwhelming evidence" of most of the charges leveled at the industry — that it conspired to violate, and indeed violated, federal racketeering laws.

"In short," she wrote, "defendants have marketed and sold their lethal product with zeal, with deception, with a single-minded focus on their financial success, and without regard for the human tragedy or social costs that success exacted."

Long awaited, the ruling was a significant, if incomplete victory for the government and for anti-smoking advocates.

Eight years ago, the industry agreed to pay states $246 billion in compensation for the public money spent on treating the health effects of smoking. A year later, the Clinton administration's Justice Department filed its racketeering suit in federal court. Anti-tobacco activists predicted that government and private litigation would cripple the industry.

But after yesterday's decision, and last month's Florida Supreme Court decision overturning a $145 million judgment against tobacco makers, some said the industry may not be as threatened as it once appeared to be.

"This was the last big really major case against the industry. Individual smokers will continue to sue, but that's going to amount to static. I don't think there's going to be another big case like this," said Mary Aronson, a tobacco litigation analyst in Washington.

Other experts said the industry was not yet out of the woods. If the decision is appealed by either side, and the appeals court limits on the penalties are overturned, Kessler's decision could provide the groundwork for imposing staggering fines.

The Justice Department lawsuit originally sought $280 billion in what the government argued were the tobacco industry's ill-gotten gains from the marketing of a harmful, addictive product. But the U.S. Court of Appeals for the D.C. Circuit ruled that under federal civil racketeering law, a company could not be forced to turn over past profits as a way of preventing future misconduct.

The Justice Department subsequently proposed a $130 billion penalty to pay for anti-smoking programs, but it scaled that back to a total of $14 billion — $10 billion to help people quit smoking and $4 billion to educate the public about the risks of smoking, though the Justice Department's own expert said $130 billion was needed.

Critics inside and outside the department saw the huge cut as part of a political effort to insulate the companies from a larger penalty and several accused Robert McCallum, an associate attorney general appointed by President Bush, of trying to weaken the case. An internal Justice Department investigation cleared him of wrongdoing, saying he was supporting a figure he thought could be sustained on appeal. McCallum is now U.S. ambassador to Australia.

The Associated Press contributed to this report.