PITTSBURGH — Major world leaders formed themselves into a new board of directors for the global economy today, vowing to overhaul lax financial regulations and work harder to control dangerous imbalances that contributed to a financial meltdown.

President Barack Obama and the other leaders declared that going forward, their meetings of the Group of 20 nations would be the primary way of coordinating global economic policy. That group will take over the job that had been done for more than three decades by a smaller group of the wealthiest countries known as the G-8.

"The old system of international economic cooperation is over. The new system, as of today, has begun," declared British Prime Minister Gordon Brown.

He said that the G-20, which includes not only developed nations but fast-growing emerging markets such as China, Brazil and India, would become the "premier economic organization for dealing with economic management around the world."

To show their resolve, the G-20 nations held a series of discussions today to discuss the thorny problems still confronting the economy and to search for ways to make sure that the financial excesses that led to the worst global downturn since the Great Depression were not repeated.