ATLANTA — President Obama on Tuesday challenged world powers to accelerate the global response to the Ebola outbreak that is ravaging West Africa, warning that unless health care workers, medical equipment and treatment centers were swiftly deployed, the disease could take hundreds of thousands of lives.

“This epidemic is going to get worse before it gets better,” Mr. Obama said here at the Centers for Disease Control and Prevention, where he met with doctors who had just returned from West Africa. The world, he said, “has the responsibility to act, to step up and to do more. The United States intends to do more.”

Even as the president announced a major American deployment to Liberia and Senegal of medicine, equipment and 3,000 military personnel, global health officials said that time was running out and that they had weeks, not months, to act. They said that although the American contribution was on a scale large enough to make a difference, a coordinated assault in Africa from other Western powers was essential to bringing the virus under control.

“Everyone realizes that no one group or one country or one organization is going to be able to tackle this,” Dr. Jim Yong Kim, the president of the World Bank and an expert in infectious diseases, said in a telephone interview hours after the bank’s board unanimously approved a $105 million grant as part of its previously announced assistance to the most affected of the countries. He praised the American effort as “extremely encouraging,” but said it remained unclear how the United States would coordinate its effort with relief groups. “This is all being put together on the fly,” he said.