An expected Cabinet-level meeting on Monday to discuss the issue was called off. A new date was not immediately scheduled, said one trade lobbyist.

After a round of meetings, Fischler told reporters that U.S. Trade Representative Robert Zoellick and Agriculture Secretary Ann Veneman were "in a kind of decision-making process" and assessing the likely impacts of a challenge. They gave no indication when the United States would act, he said.

"It was the right moment to tell the responsible authorities what we see as the negative consequences," Fischler said. A U.S. challenge might arouse a consumer backlash in Europe, he said, as well as disrupt European Parliament review of the new rules.

Like other EU officials, Fischler urged the United States to set aside thoughts of a challenge while the 15-nation EU revised its biotech rules.

"The question could be asked, would not it be worth waiting three or four months? Then you will see our system works," Fischler said. "Then we could avoid a lot of damage on both sides of the Atlantic."

British Agriculture Minister Margaret Beckett, who met Veneman separately, said she argued there were "sufficient other interests" to dissuade a U.S. challenge.

Belgian Foreign Affairs Minister Annemie Neyts-Uytterbroeck told Reuters that she warned Veneman a WTO case "could be a major foreign relations battle" when the EU was moving to end its moratorium.

"We also encouraged them to encourage (U.S.) companies to start filing for authorization for bringing GMO products" into Europe, Neyts-Uytterbroeck said.

Three applications were pending for consideration under the new EU review system, Fischler said.

Besides the moratorium, U.S. officials have criticized upcoming EU requirements for special labels on GMO foods and documentation to trace back the source of a food.

"This was not discussed in detail," Fischler said, adding that labeling or traceability "is our right." Nor, he said, would the requirements operate as a de facto trade barrier or impose a financial burden. "It seems to me exaggerated to say this."

Veneman has met four European officials in the past week to discuss world trade talks on agriculture and to stress U.S. impatience for EU action on biotech foods.