WASHINGTON — Against the backdrop of memorials to historic atrocities, a group of foreign policy experts, among them Secretary of State Hillary Rodham Clinton, gathered at the Holocaust Memorial Museum on Tuesday to consider modern threats of genocide and how to prevent them.

With the specter of mounting violence in some countries, the threat of future mass killings was a prime concern.

“The United States and our partners must act before the wood is stacked or the match is struck,” Mrs. Clinton said, “because when the fire is at full blaze, our options for responding are considerably costlier and more difficult.”

She and others who appeared at the symposium focused on the practical steps that might be taken to identify places where genocide can occur and to pre-empt it. The risk of mass killings goes up in nations where resources are scarce and governments are fragile or autocratic, they agreed.