By the early hours of Saturday, representatives of the 193 countries who have negotiated here for nearly two weeks had not yet approved the deal and there were signs they might not. But Mr. Obama, who left before the conference considered the accord because of a major storm descending on Washington, noted that the agreement was merely a political statement and not a legally binding treaty and might not need ratification by the entire conference. Negotiators have all but completed a sweeping deal that would compensate countries for preserving forests, and in some cases, other natural landscapes like peat soils, swamps and fields that play a crucial role in curbing climate change. Environmental groups have long advocated such a compensation program because forests are efficient absorbers of carbon dioxide, the primary heat-trapping gas linked to global warming. Rain forest destruction, which releases the carbon dioxide stored in trees, is estimated to account for 20 percent of greenhouse gas emissions globally.