The Group of 20 rich and developing economies, fresh from a triumphant show of unity at Pittsburgh, faces months of deal-making and communication to markets that will test its credibility as the premier global forum for economic cooperation.

"It worked," G20 leaders said early yesterday of their response to the global financial crisis.

"Our forceful response helped stop the dangerous, sharp decline in global activity and stabilise financial markets," they said in the final summit communique.

The leaders agreed their summits would supplant those of the Group of Seven rich nations as the high table of global policy making, promising to give rising powers such as China more say in rebuilding and guiding the world economy.

While G7 states were right to accept the inevitable dilution of global economic power caused by the rapid industrialisation of poorer countries, analysts said the size and diversity of the group would probably complicate policy coordination.

"There are a lot of cooks in the kitchen... I would wait until we declare victory," said Simon Johnson, a former chief economist of the International Monetary Fund. "They have to prove their value and legitimacy."

Challenges to the group's new mantle lie everywhere, from inertia on climate change to scepticism in global financial markets.

G20 nations will remain in the spotlight at the IMF meetings in Istanbul next month, another summit in South Korea in November and the UN climate change talks in December.

Markets were unlikely to react to the support in Pittsburgh for a US-led push to reshape the global economy by smoothing out huge surpluses in exporting powerhouses such as China and large deficits in big importers such as the United States.

"Any indication of unity will move the dollar," said Christopher Low, an economist in New York. "But disagreement will rule and that should result in no market reaction."

G20 leaders agreed to work together to assess how domestic policies mesh and to evaluate whether they were "collectively consistent with more sustainable and balanced growth".

Countries with sustained, significant surpluses – a description that fits China – pledged to strengthen domestic sources of growth. By the same token, countries with big deficits – such as the US – pledged to support private savings. The leaders agreed to shift some voting rights at the IMF to under-represented countries from rich ones, another sign of the changing balance of power.