After criticism that it was slow and ineffective in the crucial early months of the Ebola crisis, the World Health Organization said Monday that it would overhaul the way it deals with epidemics.

“The world, including W.H.O., is ill prepared for a large and sustained disease outbreak,” the organization said in a statement by Dr. Margaret Chan, its director general, and by its deputy director and regional directors.

Amid an overall contraction of the organization’s budget in recent years, there have been sharp cuts to its outbreak and emergency response departments. In the statement, Dr. Chan and her colleagues said that trend would be reversed.