In a report to be released Wednesday, Oxfam International highlights three American commodity crops vulnerable to lawsuits and eight agricultural products in the European Union that could be sources of cases.
Several independent experts agree with Oxfam's assertion that complaints could be brought against the United States' corn, rice and sorghum programs, while the 25-country European Union could be challenged on subsidies for tomatoes, tobacco, butter, wine and spirits, citrus juices and processed fruits like canned peaches and pears.
According to the report, the subsidies for the 11 crops and products noted by Oxfam total $9.3 billion for the United States out of the country's $19.5 billion in subsidy payments, and $4.2 billion for the European Union out of $44.8 billion, on an annual basis.
Oxfam, a nongovernmental advocacy group involved in world poverty issues, has lobbied strenuously for rich countries to reduce agricultural subsidies so that developing countries in Africa and elsewhere can better compete and grow their economies. But several outside experts agree that more cases are likely if meetings of the World Trade Organization next month in Hong Kong do not produce a substantial agreement toward reducing so-called trade-distorting subsidies.
Brazil's successful challenges to the European Union's sugar program and parts of the United States' cotton program have opened the door for more challenges before the W.T.O., trade experts say. The European Union unveiled an overhauled sugar program last week that cuts support prices 36 percent.
"Those cases point out some of the vulnerabilities that both the E.U. and the U.S. have with some of their present farm programs," said Clayton Yeutter, a former secretary of agriculture and United States trade representative. If negotiations do not produce progress, "it would not be surprising to see additional W.T.O. dispute settlement challenges of this nature," he said.
The talks in Hong Kong are part of a round of trade discussions that began in 2001 in Doha, Qatar. They were termed a "development round," meant to lift the world's poor nations out of poverty by giving their farmers better access to developed world markets.
American trade officials said on Tuesday that they could not comment on the accuracy of the Oxfam estimates, but that the United States is trying to eliminate the kinds of farm subsidies that could run afoul of the W.T.O. rules.
"The very subsidies that they're concerned about are the ones that we're proposing to eliminate," said Christin T. Baker, a spokeswoman for the United States trade representative, Rob Portman.
Anthony Gooch, a spokesman for the European Commission in Washington, said he could not comment on the Oxfam report until European officials had a chance to study it.
Officials from the United States, Europe and major developing countries, like Brazil, are trying to salvage a framework before the talks in Hong Kong. Mr. Portman will leave for Geneva on Thursday for talks that will last until Sunday.
In recent weeks, preparatory trade talks stalled after the European Union failed to match an offer by the United States to lower some trade-distorting subsidies by 60 percent over five years and eliminate them by 2013. Oxfam and other advocates of reducing subsidies have called even the American proposal inadequate and misleading.
The United States and the European Union are still far apart on agricultural trade barriers. The United States proposal calls for much deeper cuts in farm tariffs than European officials have been willing to support. And large developing countries are reluctant to make commitments on opening markets for services and industrial goods unless the wealthy countries do more to open their farm markets.
In the last year, some countries have threatened legal action against American farm programs. Uruguay has been preparing a challenge to American rice subsidies, while Canadian corn growers have been clamoring for their government to fight the sale of American corn in Canada at prices they say are lower than the cost of production.
The Canadian International Trade Tribunal concluded two weeks ago that there was "a reasonable indication that the dumping and subsidizing of unprocessed grain corn have caused injury to the domestic industry." Mike Johanns, the United States agriculture secretary, and Mr. Portman said in a joint response that "U.S. corn exports pose no threat to Canadian corn growers."
The United States corn program is more vulnerable than ever to a trade challenge, trade experts say. Huge harvests the last two years and the lowest prices since the late 1990's are resulting in record subsidy payments to farmers. The United States paid $26.8 billion in corn subsidies the last five years, the most for any single American farm program.
"If there were ever a time for another country to go after our corn program, this is it," said Kenneth Cook, president of the Environmental Working Group, a research organization based in Washington that has criticized farm subsidies. "It is exactly the kind of conditions that prompted Brazil to go after our cotton program."
Eleven corn exporters, including Argentina, Ecuador and South Africa, could have legitimate cases as well, the Oxfam report concluded. And in the case of rice, Mexico, India and Thailand are among 13 countries that could file cases against the United States. Without a formal suit, Mexico has struggled to prevent rice from the United States from being sold at what it says are unfair prices that are damaging Mexican producers. A World Trade Organization panel ruled on Tuesday that Mexico unfairly imposed antidumping tariffs on American rice in 2002.
While the European Union also has programs laden with heavy subsidy payments for farmers of traditional crops like sugar, it is at least as vulnerable for programs designed to encourage the processing of fruits and vegetables into finished products, trade experts said. The European Union provides millions of euros in such subsidies.
So far, no formal challenges on major crops have been filed since the Brazilian won its cases in 2004 and this year. Pedro de Camargo Neto, a former lead farm trade negotiator for Brazil, who led his country's cotton and sugar cases, said he is surprised other countries have not capitalized on the Brazilian precedents.
Fear of retaliation could be part of the reason, Mr. Camargo said in a telephone interview. "Governments are afraid to challenge the Empire."
In one case, Walter Bastian, the United States deputy assistant secretary of commerce, met with Uruguayan officials in August and persuaded them to wait until after the Hong Kong meetings to file a rice complaint.
Most countries see trade negotiations as a faster road to agricultural reform than litigation, which is costly and can drag on for years. But the failure of the Doha talks will probably lead more developing countries to use the W.T.O.'s dispute settlement process, said Gawain Kripke, senior policy adviser for Oxfam. "This hasn't been in their toolbox in the past," he said. "Brazil has shown that these cases are winnable."