When world leaders gather in Italy for their G-8 summit on Wednesday, the global economic crisis will be topic A, B and C. Yet even with the clear urgency that the economic meltdown demands, it is part of a much broader set of interrelated international challenges. For future meetings, the agenda of the G-8 and the group itself will have to expand in order to keep up with the times.

For world leaders, the road to Italy will continue on to Pittsburgh for the more inclusive G-20 summit in September. There is already a growing interplay between the two summits -- an indicator perhaps of an inevitable evolution.

The need for such changes stems from the very nature of the G-8. In the realm of high-level diplomacy, this is the world's most exclusive club. Its chief purpose is to gather presidents and prime ministers from the so-called "leading industrial powers" of the United States, Canada, Japan, Britain, Germany, France, Italy and Russia. Because it brings together top leaders from a select group of economic heavyweights, its consultations are an inherently important focal point for global politics.

On the other hand, because the G-8 is so dominated by Western nations and excludes newly powerful countries such as China, India and Brazil, it has built-in limitations too. The G-8 tries to compensate by meeting with several of these emerging powers for a portion of their summit schedule. But leaders of those countries are bound to bristle at this junior status rather than full membership. In fact, they have already started to.

Perhaps the more effective forum is the more inclusive G-20, whose consultations -- which used to be among finance ministers -- have kicked into a higher gear since the economic crisis. The Pittsburgh meeting will mark its third presidential summit in less than a year.

For each of these meetings, the protocol, security and resulting communiques are all carefully choreographed. The impressive pageantry, though, should not distract leaders from the serious business at hand. With a foreign policy agenda that is bursting with urgent problems, world leaders should make every effort to deliver significant action rather than hedged and watered-down statements. Hopefully, global public sentiment will similarly expect serious responses to serious problems.

Whether the issue is climate change, sustainable energy, nuclear proliferation or terrorism, the need is the same: international cooperation on steps to tackle the problem. The U.N. Security Council resolution on North Korea's recent nuclear and missile tests is a good example of strong international response to the provocative actions of one country. But it shouldn't take a dramatic event like North Korea's tests to prompt a strong response. In other words, diplomacy as usual will let major global problems grow worse, rather than lessening them.

Because they bring together top leaders, the "G" groupings hold particular promise as avenues for more effective cooperation. Unlike treaty-based institutions, such as the United Nations and World Trade Organization, they lack legal authority. Essentially they are nothing more than series of meetings.

Yet this may not be a handicap. Today's global problems demand political and policy steps, and not just legally binding measures. The test of leadership in today's shrinking, interconnected world is to overcome differences and take decisive (often difficult) action. Here again, the G groupings could be ideally suited. Those who have watched such discussions closely often note that when presidents and prime ministers deal with each other "leader to leader" they can devise approaches that take each other's domestic political pressures into account.

Looking toward the G-8 and G-20 summits, one can't help wondering what will become the key grouping at the apex of international politics. Will leaders continue to gather in two different combinations?

The view from some foreign capitals is to reject any notion that a few select nations can act on behalf of everyone else. As Americans know from recent experience, a command-and-demand approach to international leadership is not terribly effective. On the other hand, too much deference leads to the diplomacy of the lowest common denominator -- with problems being kicked down the road.

The key will be for leaders to strike the right balance between sensitivity and decisiveness. They must complement their consultations with extensive diplomatic outreach to the rest of the world -- the G-172, some call it -- so other nations understand they have more to gain than lose from heightened cooperation between pivotal powers.