The G-20 -- short for Group of 20 Finance Ministers and Central Bank Governors -- emerged during the Asian financial crisis of the 1990s, as finance ministers cast about for ways to prevent economic troubles in one place from spreading to the next.

After 10 years, the G-20 amplified its ranks, with heads of state meeting alongside those ministers as the global economy grew increasingly complex and dangerous.

"It's basically a meeting of the financial leadership of a group of 20 significant countries to discuss international economic and financial issues," said Chester Spatt, chaired professor in finance at Carnegie Mellon University's Tepper School of Business.

If that sounds dry, consider the stakes: the G-20's member-nations account for about 90 percent of the planet's gross domestic product, 80 percent of the world's trade and roughly two-thirds of its population.

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Pittsburgh's selection as the location for the organization's next summit promises the logistical nightmare of moving 20 heads of state or their proxies in and out of the city. At the same time, say financial experts, the meeting will deal with the ongoing nightmare of a global economy spiraling into recession, as national leaders cast about for a way to prevent a full-blown world depression.

"I think it's clearly saying these issues are first-order issues, and that it's important for the highest leadership of this country to be engaging in these issues," said Mr. Spatt.

So first-order have G-20 issues become that its previous meeting in London last month spurred massive demonstrations by groups protesting economic globalization and global warming. Pittsburgh's gathering is likely to draw similar skepticism from some quarters.

"To be blunt, they're the ones that created the mess. To suggest they're going to get us out of it is a little ridiculous," said David Solnit, a California-based economic activist, who played a leading role in the street battle to shut down the World Trade Organization when it met in Seattle a decade ago.

Mr. Solnit said he's not likely to come here, but predicts that the G-20 meeting could spur protests in a variety of venues.

While it is early to sort out a detailed agenda for the meeting, still four months away, much of the framework for the Pittsburgh summit was laid out in London last month, when heads of state gathered there. The United Kingdom currently holds the chairmanship of the G-20.

That meeting, punctuated by French President Nicolas Sarkozy's threat to walk out if an agreement were not reached on dealing with the economic meltdown, produced a four-point agenda likely to be dealt with here in September.

First, leaders are likely to take the measure of the sputtering economy that brought them together, first in November in Washington and again last month in London.

"They're going to get a readout in September on whether we've stopped the trough," said Colin Bradford, a former Clinton administration economist and currently a visiting scholar at Washington's Brookings Institution. "Are we flattening out? Are we recovering? What's happening?"

From that readout, leaders will likely deal with a second agenda item laid out in London: determining whether two agencies charged with overseeing world finance, the International Monetary Fund and the Swiss-based Financial Stability Board, have set up the structures needed to oversee financial institutions that ran fiscal riot in the lead-up to the recession.

Various countries have pledged a combined $1 trillion for the IMF, a quadrupling of its funding, so it can provide stopgap loans to countries with bleeding economies, lest they collapse and set off a domino effect of regional economic failures. Pittsburgh, said Mr. Bradford, could be the place where the leaders of those countries determine whether those pledges can be met.

Mr. Spatt, the CMU economist, suggested that recent plunges in the stock and bond markets could leave some wealthier G-20 nations reticent to write checks to the IMF, such as the U.S. pledge of $100 billion. "Events over the last 10 days in the capital markets illustrate how precarious the budgetary situation is in some of the most advanced countries, including the United States," he said.

Then will come the discussion of the G-172. That's the rest of the world, the non- and quasi-industrial nations in the developing world.

While the IMF role has been to put out fires, the G-20 leaders determined in London that some structure must be set in place to build economies in the developing world or risk a dangerous widening of the wealth gap as the global economy recovers.

If September sees an end to the economic trough in the world that comprises the G-20, there could be talk about pressing for loans to the less-developed world from institutions such as the Asian Development Bank or the World Bank.