If Daniel Sumner's actions be treason, as some of his critics contend, then he is glad the most has been made of it.

Sumner, an agricultural economist at the University of California at Davis, played a key role in an international trade case that is shaping up as one of the most significant defeats the United States has ever suffered on the trade front. An analysis that he wrote helped frame a preliminary decision issued two weeks ago by a World Trade Organization panel, which held that the federal subsidies paid to U.S. cotton farmers violate WTO rules because they cause overproduction, drive down world prices and impoverish farmers in developing countries.

Since Sumner served as a paid consultant for Brazil, which brought the case against Washington, he is being reviled as a traitor by some U.S. farmers. Leaders of some farm groups, furious at Sumner for helping a foreign government win a victory that could end agricultural subsidies in their current form, are vowing to retaliate by cutting off funding for other work that he does.

"He joined forces with the enemy to cut the heart out of our farm program," said Don Cameron, vice chairman of the California Cotton Growers Association and chairman of the California Tomato Growers Association Inc. He said such an act was "unethical" because Sumner is an employee of California's public university system. "There are research projects that he's been involved with in the past that we'll direct elsewhere."

To opponents of farm subsidies, the treatment Sumner is getting underscores what they have been saying all along: that well-organized and well-heeled interest groups benefit from the federal payments and will go to great lengths to protect the system despite evidence of the harm inflicted on some of the world's weakest citizens. The World Bank and other international institutions have long complained about the impact of subsidies on Third World farmers, but Sumner's cotton analysis was unusually detailed and precise.

"He's done a real service, not just to Brazil, but to the world, by clarifying the role that U.S. farm programs are having globally," said Gawain Kripke, senior policy adviser at Oxfam, the international aid group. Although U.S. officials have said they will likely appeal the WTO ruling, Oxfam hopes the decision will increase pressure on the United States, the European Union and Japan to scrap subsidies that effectively guarantee a minimum price for certain crops. The rich nations' reluctance to cut assistance to their farmers has been a major sticking point in global negotiations to lower trade barriers worldwide.

Dale E. Hathaway, a former undersecretary of agriculture, said Sumner "did an honest job of trying to assess the impact of these subsidies, and there are some people who are not particularly enthused about having a serious job of assessing the impact, because it makes them look bad." Noting that Sumner served as assistant secretary of agriculture for economics in the administration of President Bush's father, Hathaway added that it is "ironic that Dan, who is a good, conservative, traditionally trained economist . . . should be accused of all these things that people are talking about."

The man at the center of this furor is, by the accounts of both fans and critics, a pleasant, soft-spoken academic. Sumner said that like many economists at universities, he is not favorably disposed toward farm subsidies in general, because he sees little rationale for protecting farmers from market forces, and he believes that some of the goals subsidies are supposedly aimed at -- preserving rural communities, for example -- could be achieved much more effectively by using other programs.

But that wasn't his motivation for accepting the Brazilian request last year to analyze the impact of the cotton program, he said. Nor, he maintained, was it the consulting fee, which he said was in the "tens of thousands" of dollars, because he turns down many such opportunities. Rather, he said, "my view was, and is, that it's important to have the very best information" for major cases in which the Geneva-based WTO adjudicates disputes between nations.

"I think the WTO is incredibly important, for the world as a whole and for agriculture," he said. "I think it helped the decision-making to have someone familiar with U.S. farm programs, and who had analyzed them for a while, to be involved in the case." The only way to do that, he added, was to work for one side or the other, and though he would have gladly given the same information to the U.S. Agriculture Department or trade representative's office, "I suspect they wouldn't have wanted it used."

The result was a study filled with mathematical equations and symbols, using Agriculture Department data, the most damning portion of which was an estimate showing how big a role subsidies had played on world markets in 1999-2002. During that period, cotton prices slumped to about 30 cents a pound, and Sumner calculated how the nation's 25,000 cotton farmers would have behaved if the $3 billion to $4 billion a year in domestic and export subsidies had been removed.

He concluded that the United States, the biggest exporter of cotton, would have shipped about 41 percent less cotton abroad; that would have raised the world price about 12.6 percent.

U.S. trade officials defending Washington's case at the WTO attacked Sumner's analysis as faulty, but a much more vituperative reaction came from farm organizations whose California representatives went to Sumner's university last summer to confront him and university administrators.

"If this was governmental or military related, it might be called treason and court martial proceedings would be in order," Earl P. Williams, president of the California Cotton Growers Association, was quoted as saying in the Western Farm Press. "Furthermore, I would hope that anyone that supports the UC system financially would step back and question continued support until this issue is resolved."

Inflaming the farm groups' anger, some of their officers said, was a sense of betrayal that an economist of Sumner's reputation and previous official position would defect to the opposing side. They understand that a professor has a right to academic freedom, said Charlie Hoppin, chairman of the California Rice Industry Association, but "other than buying his fine mind, [the Brazilians] bought very impeccable credentials."

Now that the WTO has ruled against the U.S. position, "we're just as mad as we were earlier, if not madder," Cameron said of the cotton growers group.

The message has been received loud and clear by Neal Van Alfen, dean of the College of Agricultural and Environmental Sciences at UC-Davis, who said the amount of money farm organizations provide for research at the university is "significant."

Van Alfen said Sumner "has the right, and it's an important right" to use his academic expertise as he did by working for the Brazilians, and be paid for it, especially since he was careful to spend only vacation time doing so. But, the dean said, "I question his judgment. It's a matter of, in any organization, if you have close working relationships with a broad group of people, you want to think twice about developing relations with their competitor, and doing it in such a public way."

Sumner, however, is unrepentant. "I'm trying to do the best economics and put it into the system," he said.

Likening the growers' threats to witness tampering, he said with a chuckle: "What is this, the mafia or something? Think of it as a criminal case, and one side says, 'We'll put pressure on this guy not to participate.' That's not right, is it?"

The World Trade Organization ruled against U.S. subsidies to cotton farmers. Daniel Sumner, a professor at UC-Davis, wrote an analysis for Brazil that was important in the recent WTO ruling against U.S. subsidies. Sumner was an undersecretary of agriculture under President George H.W. Bush.