As member states wrangled over the final text on Thursday, US President George W Bush said India and China "must" be involved for success of any effort to fight global warming.
The summit host, German Chancellor Angela Merkel, however, said though she was "very, very satisfied" with the agreement the accord was a compromise as it fell short of her hopes for a binding deal.
"Many countries moved on this issue," Merkel said, adding that the accord gave impetus to negotiations beginning in Bali in December to find a successor to the UN-backed Kyoto Protocol on capping greenhouse gases that expires in 2012.
"The very best we could achieve has been achieved," Merkel said.
Bush earlier said, "Nothing is going to happen in terms of substantial reduction unless China and India participate."
"If we want them (India and China) at the table, it is important that we give them the opportunity to set an international goal," he added.
India has held that countries responsible for creating the problem of climate change should come out in a big way to solve this issue. India argues that the greenhouse gas emissions of developed countries even today are many times more than developing countries like India.
"The US will be actively involved, if not taking the lead, in a post-Kyoto framework, a post-Kyoto deal," Bush said after talks with British Prime Minister Tony Blair on the sidelines of the summit.
Blair had said he was holding out hope for a pact on significant emission cuts at the summit that would pave the road to a strong deal at a UN meeting Bali, Indonesia in December as the successor to Kyoto.
China, India and other developing countries, which have been invited to participate in the summit, are not required to make targeted emissions cuts under Kyoto.
The United States, the only G-8 country that has not ratified the Kyoto Protocol, has flatly rejected any mandatory targets in a new pact.
Bush surprised many last week by offering a counter-proposal in which the United States and up to 14 other big emitters would agree by the end of next year to "a long-term global goal" for reducing greenhouse gases.
Merkel has insisted that any agreement come within a UN-framework, a condition Bush warmed to at the summit.
Bush sharply rejected accusations that Washington was doing nothing to tackle climate change, telling reporters that US greenhouse gas emissions had declined in the last year despite the fact that the economy had grown.
"We are taking steps necessary to be good stewards of the environment and at the same time advance technologies," he said.