The A.U. has 2,270 troops in western Sudan attempting to stop fighting between rebels and Arab militias, but has plans to increase that number to more than 12,300. It has asked for $723 million to help finance and equip the Darfur operation.
Snyder said the violence in Darfur was slowing, but that the only way to end it was to deploy a large A.U. force supported by the North Atlantic Treaty Organization.
"The truth is the A.U. was looking for outside support and when you are looking at support on this kind of scale we need an organization that can do it, such as NATO," Snyder told The Associated Press.
The peacekeeping operation is a critical test of international commitment and Africa's resolve to end conflicts in the world's poorest continent, A.U. Commission Chairman Alpha Oumar Konare said.
"If Sudan were to collapse then the entire continent of Africa, with nine countries bordering Sudan , will also suffer and collapse," he told the donors.
"We are running a race against time," said U.N. Secretary-General Kofi Annan, who was at the conference along with NATO Secretary General Jaap de Hoop Scheffer and the European Union's foreign policy chief Javier Solana.
"If violence and fear prevent the people of Darfur from planting and growing crops next year, then millions will have to be sustained by an epic relief effort which will stretch international capacity to the maximum," Annan said.
The A.U. is seeking six helicopter gunships, 116 armored personnel carriers and other equipment to help it deploy more peacekeepers in Darfur, the scene of one of the world's worst humanitarian crises.