Twenty world leaders launched extraordinary summit talks Friday on the economic crisis gripping the globe, searching for ways to limit the current carnage and prevent future calamities. Big talk filled the air, but the results were likely to be more modest. The summit of leaders from both big industrial nations and developing countries began with a White House dinner Friday night and was to conclude Saturday after a day of private talks at the stately National Building Museum in Washington. The leaders are expected to set up working groups to devise the details of their proposals. They also aim to set a date for the next meeting, likely to be held after Bush leaves office in January and President-elect Barack Obama has taken over. Obama is staying away from this summit but has designated high-level representatives to meet with leaders on the sidelines. .