Nearly one-fourth of United States senators on Monday wrote President George W Bush seeking his participation in discussions on global warming, as a United Nations conference meets in Montreal. Democrat Jeff Bingaman, Republican Olympia Snowe and 22 colleagues said the US has a legal obligation, under a UN treaty, to participate in the negotiations in a constructive way. "In our view, a deliberate decision by the administration not to engage in such discussions, solely because they may include the topic of future binding emissions reductions requirements, is inconsistent with the obligations of the United States as set forth in the UNFCCC treaty. "In any event, the United States should, at a minimum, refrain from blocking or obstructing such discussions amongst parties to the convention, since that would be inconsistent with its ongoing treaty obligations," the letter said.