A loose-knit populist campaign that started on Wall Street three weeks ago has spread to dozens of cities across the country, with protesters camped out in Los Angeles near City Hall, assembled before the Federal Reserve Bank in Chicago and marching through downtown Boston to rally against corporate greed, unemployment and the role of financial institutions in the economic crisis.

With little organization and a reliance on Facebook, Twitter and Google groups to share methods, the Occupy Wall Street campaign, as the prototype in New York is called, has clearly tapped into a deep vein of anger, experts in social movements said, bringing longtime crusaders against globalization and professional anarchists together with younger people frustrated by poor job prospects.

“Rants based on discontents are the first stage of any movement,” said Michael Kazin, a professor of history at Georgetown University. But he said it was unclear if the current protests would lead to a lasting movement, which would require the newly unleashed passions to be channeled into institutions and shaped into political goals.