PITTSBURGH — Leaders of the world's major economies are coming together on reforms to rein in huge bank bonuses, toughen financial regulations and guard against the dangerous imbalances that contributed to the worst global downturn since the 1930s.

In the process, the Group of 20 countries decided they will serve as the board of directors on decisions for the global economy, taking over a role performed for more than three decades by a smaller group of wealthy nations.

President Barack Obama initiated the move to transfer the responsibilities of economic coordination from the Group of Eight major developed countries — the United States, Japan, Germany, France, Britain, Canada, Italy and Russia — to the bigger G-20.

The G-20 also includes major emerging economies such as China, Brazil and India and underscores how much the world has changed since a small club of wealthy, industrial countries began meeting in the mid-1970s in an effort to respond to oil shocks, stagflation and other economic crises of that period.

The decision was to be announced today as Obama and the other leaders prepared a joint action plan to address regulatory overhaul and efforts to achieve more balanced growth.

The Pittsburgh meeting marked the third G-20 leaders summit in less than a year.