The surprise vote, 61 to 37, forged an unlikely alliance of the most ardent anti-tobacco Democrats, who wanted to punish the companies, with some of the senate's most conservative Republicans, who oppose the overall bill.

It was a setback to Arizona Republican senator John McCain's legislation, which aims to transform the cigarette business.

"Today we had a defeat. There will be more victories and more defeats as we go through this very difficult process," McCain said. But he predicted that the senate would ultimately pass a bill to combat teen-age smoking.

The amendment by New Hampshire Republican Judd Gregg and Vermont Democrat Patrick Leahy would eliminate the section of the McCain bill that gives tobacco companies an annual $8 billion limit on the amount they would have to pay in legal judgments from civil lawsuits.

The vote wason a procedural measure, so technically the senate must still formally adopt Gregg's amendment, but McCain said that was a routine matter and he considers it adopted.

Gregg had called the caps "ironic and absurd," and said granting any form of immunity to tobacco companies represented a "deal with the devil."

Gregg was opposed by the White House, which backed McCain's approach, but strongly backed by C. Everett Koop, a former US Surgeon General and former Food and Drug Administration chief David Kessler.

"I can't think of any redeeming feature of a tobacco company, or indeed a tobacco executive," said Koop.

Legal liability for tobacco companies is one of the most controversial and emotional elements of the tobacco reforms. Many lawmakers were reluctant to grant any concessions to companies whose products ultimately kill a third of its customers.

But some of the people who voted for the Gregg-Leahy amendment were actually opponents of the McCain bill, and it is unclear whether the liability changeswill dimish McCain's chances of getting a winning coalition for the final package.

"What was just passed on the senate floor is tougher than what was there," said Massachusetts Democrat John Kerry. "And some of the people who joined in that effort to make it tougher are people who want to kill the bill. There is something perverse in that."

The White House and McCain included limited legal protection in the bill hoping to lure the companies to cooperate rather than try to undermine a new law through prolonged court challenges. The tobacco companies have waged an expensive advertising campaign to try to defeat the bill.

Working with the White House, McCain had recently modified the liability provisions. He raised the annual cap to $8 billion from $6.5 billion, and dropped all other obstacles to suing tobacco companies.

In addition, the legal protections would be contingent on the companies cooperating with certain public health goals and advertising restrictions. McCain said he would have to modify theadvertising portions of the bill. He did not specify how.

President Bill Clinton had lobbied to keep the cap.

"If a cap that doesn't prevent anybody from suing the companies and getting whatever damages a jury awards will get tobacco companies to stop marketing cigarettes to kids, it is well worth it for the American people," Clinton wrote senate leaders this week.