WASHINGTON — The president of Liberia, Ellen Johnson Sirleaf, has implored President Obama for help in managing her country’s rapidly expanding Ebola crisis and has warned that without American assistance the disease could send Liberia into the civil chaos that enveloped the country for two decades.

In a letter on Tuesday to Mr. Obama, Ms. Johnson Sirleaf wrote that “I am being honest with you when I say that at this rate, we will never break the transmission chain and the virus will overwhelm us.” She requested 1,500 additional beds in new hospitals across the country and urged that the United States military set up and run a 100-bed Ebola hospital in the besieged capital, Monrovia.

Infectious-disease experts have sharply criticized as inadequate the Obama administration’s response to the Ebola crisis, particularly in Liberia, a country founded by freed American slaves. Global agencies like the World Health Organization and the United Nations have also come under criticism for responding too slowly to the Ebola outbreak.

The epidemic has taken an estimated 2,218 lives out of 4,366 cases in West Africa. So far more than 1,000 people have died of the virus in Liberia.