The new U.S. farm bill might violate World TradeOrganizationrules against trade-distorting subsidies, major U.S.business groups said on Monday in an appeal to lawmakers to revampthe bill, which is already facing slim odds of passage.

An adverse decision by the WTO could expose U.S. exports toretaliatory tariffs if there is a challenge. It would be an ironicturn, since the farm bill was intended in part to resolve a WTOruling against U.S. cotton subsidies.

Leaders of the Senate and House Agriculture committees had noimmediate response on Monday to the assertion by the U.S. Chamberof Commerce, National Association of Manufacturers and NationalForeign Trade Council.

"We think meeting our international obligations is an importantelement of maintaining an open trading system, from which theUnited States benefits," said Bill Reinsch, head of the tradecouncil.

In a letter, the groups said the farm bills pending in the Houseand Senate carried some of the same provisions that WTO ruledagainst in the cotton case. They said the bills each "run asubstantial risk" of violating WTO rules on farm subsidies.

A House provision that ties crop payments to actual plantings ofthe crop could "quickly invite other nations to initiate disputesettlement against the United States – and do so with good chancesof success," they said.

Brazil won the right to impose $830 million in retaliatorytariffs on U.S. goods when it won a WTO challenge of U.S. cottonsubsidies after a long-running case. It has delayed action whileawaiting U.S. reforms. Officials warned in August that theirpatience was not endless.

An analysis by the international law firm White & Case said"potential complainants include Brazil, China and Argentina." Itsaid the House provision was the most likely trigger for a WTO caseand highly likely to be ruled a violation.

A somewhat similar Senate provision would link price supports tohistorical plantings, an approach less likely to draw a challenge,said the analysis, but its high support prices could triggerpayments that exceed WTO parameters.

The Republican-controlled House is expected to vote later thisweek on a bill to cut food stamps for the poor by $40 billion over10 years. The vote could open the door to House-Senate negotiationson a compromise farm bill.

Analysts say that, ultimately, Congress is likely toextend  the 2008 farm law for a second time. The abilityto pass a new bill has stalled because of disagreements over foodstamps and farm subsidies.