Some carried signs reading "people over profits" and "debt relief now" to underscore their message to international lenders holding their spring meetings.
Following the boisterous rally modelled after "cacerolazo", pot-banging protests common in Latin capitals, the group will march to a park near the World Bank and International Monetary Fund headquarters.
"We need to have people in the street to show that we're paying attention to what the IMF and World Bank are doing," said protester Tito Bourdon, 23, of Virginia.
Protesters planned a Festival of Resistance featuring live music and tongue-in-cheek games, including Pin the Structural Adjustment on the Country.
Mobilisation for Global Justice, an umbrella group of activists behind Saturday's protest, advocates wholesale reform of the IMF and World Bank. Its core demands include greater openness in the lenders' decision-making and the cancellation of poor country debt using the bank and fund's own resources.
World Bank spokesman Damian Milverton said the street protests ought not overshadow the contributions of civil society groups and nongovernmental actors in this weekend's IMF and World Bank meetings.
An array of groups including Oxfam, ActionAid and Friends of the Earth are taking part in dialogue sessions on debt relief, water privatisation and poverty reduction.
"While the small protests do go on this weekend, we are determined to keep to our agenda of focusing on the pace of poverty reduction in the world, and the need to accelerate it," Milverton said. "We will be looking very closely in particular at what more can be done on education, on AIDS and on debt sustainability."
Scores of policemen were
deployed to monitor marches
Police barricaded several blocks of downtown Washington to control access to the lenders' headquarters and meeting sites.
Several hundred officers patrolled the streets.
Past anti-globalisation protests in Washington and other cities have included threats to "shut down" financial leaders' meetings, leading to clashes with police and arrests. This year, however, police said they expected few such problems.
Mobilisation for Global Justice has said it does not plan to disrupt the IMF and World Bank meetings. An abortion rights march, organised separately from the IMF and World Bank events on Sunday, is also expected to be peaceful.