By Richard Black
Environment correspondent, BBC News website
Washington objects to the draft's targets to keep the global temperature rise below 2C this century and halve greenhouse gas emissions by 2050.
The draft, prepared by the German G8 Presidency, says action is imperative.
With UN talks struggling to move beyond the current Kyoto Protocol targets, the G8 summit is seen as a key opportunity to regain political momentum.
Germany's Chancellor Angela Merkel has made climate a priority for the organisation, with backing from other leaders including Tony Blair.
Japanese news organisations recently reported that Prime Minister Shinzo Abe's government was also planning to push fellow G8 members for tough targets.
But at preparatory discussions between officials of the G8 countries, US negotiators have made clear their opposition to several key components of the draft.
As well as objecting to mention of targets for global temperature rise and greenhouse gas emissions, Washington is also seeking to remove a section acknowledging that the UN is the "appropriate forum" for agreeing further action.
US officials are also questioning the draft's call for the establishment of a global carbon market. Many observers believe that such a market can only be effective if there are binding caps on emissions.
"I think the real objective (of the US negotiators) is not just to keep the lid on and have nothing happen while Bush is in office, but they are trying to lay landmines under a post-Kyoto agreement after they leave office," commented Philip Clapp, president of the Washington-based National Environmental Trust, who has seen the US's proposed amendments.
"It lies in the hands of Prime Minister Blair and Chancellor Merkel, whether it's all sweetness and light or whether they are prepared to stand up and say 'I'm sorry, but the rest of the world is moving in a different direction from you'," he said.
Preparations for the 2005 G8 summit in the Scottish resort of Gleneagles also began with a climate change draft which grew weaker as discussions continued.
Leaders decided then to agree a weak document rather than leave with no agreement at all.