Other points of contention include calls for an end to all subsidies for electricity generated by fossil fuels.
Anti-war, environmental and anti-poverty groups plan to demonstrate in Pittsburgh, with one group marching from a working-class suburb in a "people's uprising". About 4,000 extra police have been drafted in.
World Bank president Robert Zoellick has urged leaders of the G20, which comprises 19 of the world's largest economies and the European Union and contains two-thirds of the global population, to set an ambitious agenda of socially responsible globalisation.
Zoellick said the G20 must avoid the narrow focus set at the last summit in London in April.
"The core message of Pittsburgh needs to be more than implementing the agenda set in London, which was mostly about financial stability or reforming bankers' bonuses. I would like the G20 to talk about responsible globalisation," Zoellick told the UK's Financial Times.
The World Bank president also warned of rising protectionism and called for a robust global response.
"We have a low-grade fever of trade tensions and the temperature is starting to rise," he said.
He urged the United States and China to settle their dispute over imports after the United States last week imposed punitive tariffs of 35 per cent on Chinese-made tyre imports - a move that prompted Beijing to lodge a complaint at the World Trade Organisation.
The summit precedes a UN climate change summit in Copenhagen in December, but environmental policy issues will almost certainly boil over into this week's meeting.
G20-member Australia on Saturday set out its policy, insisting that developing economies should not be locked into carbon-lowering targets under a new global climate pact.
Canberra has said its plan would give India and China flexibility to lower emissions through a "national schedule", potentially defusing near-stalled talks between rich and developing countries.
"We simply won't get the broad participation from major developing economies that the climate needs and that Australia, in terms of our national interest, needs," climate minister Penny Wong said of Australia's proposal.
European Commission President Jose Manuel Barroso has warned that negotiations were "dangerously close to deadlock".
In a bid to find common ground, negotiators from around 190 nations plan lead-in meetings in Pittsburgh ahead of the Copenhagen summit.