Under pressure to do more to confront the Ebola outbreak sweeping across West Africa, President Obama on Tuesday is to announce an expansion of military and medical resources to combat the spread of the deadly virus, administration officials said.

The president will go beyond the 25-bed portable hospital that Pentagon officials said they would establish in Liberia, one of the three West African countries ravaged by the disease, officials said. Mr. Obama will offer help to President Ellen Johnson Sirleaf of Liberia in the construction of as many as 17 Ebola treatment centers in the region, with about 1,700 treatment beds.