GENEVA (Reuters) - Liberia, the West African state hardest-hit by the worst Ebola outbreak in history, remains gravely short of foreign health care workers despite repeated pleas for help, a senior U.N. official said on Tuesday.

Efforts to tackle the Ebola outbreak, now six months old, have been too slow to stop the disease infecting more people than ever before and spreading from its origins in Guinea to Sierra Leone, Liberia, Nigeria and Senegal, killing over 2,800.

Without scaling up efforts to tackle the deadly hemorrhagic fever, there could be 20,000 cases in West Africa by early November, half of them in Liberia, according to a World Health Organization study published on Tuesday.

Antonio Vigilante, head of the U.N. Development Programme in Liberia, said 40,000 community workers needed to be trained and the country still had far too few foreign experts.

The opening of a new clinic in Monrovia meant Liberia now had 350-400 Ebola bed spaces but this was still far below the target of 2,000.

"We have some 50-70 cases per day. Even net of the people that die, it's very, very difficult to keep adding 30 or 40 beds or day," Vigilante told a U.N. news briefing in Geneva by telephone from Monrovia. "Even if we are at 2,000 beds two or three weeks from now, the cases we'll have in any single day may be more than that," he said, and adding new beds is of little use without the experts to manage them.

There are now some 150 foreign experts in Liberia, provided by Medecins sans Frontieres and U.N. staff, he said.


But a further 600-700 are already needed and, with the number of cases in Liberia now at 3,100 and rapidly increasing, the requirements for foreign help are only growing in the small, impoverished country.

"We have announcements that more will come but very small numbers. The African Union sent a team of medical and non-medical staff, in that team there are some 15 doctors," Vigilante said. "The American military are bringing in a camp hospital but it is for 25 beds with medical staff. And so there are still very few."

The WHO has repeatedly called for governments to send international medical teams, but the foreign effort remains largely in the hands of the charity Medecins Sans Frontieres, which has said it is overwhelmed and has pleaded for help. A co-author of the WHO study, the U.N. agency's strategy chief Christopher Dye, spoke of international pledges falling woefully short of Liberia's health needs.

"You've probably heard the stories that are coming out of major donors that we'll build a hospital and we'll spend a million dollars but it will only be 25 beds," he told reporters.

"Well, great, thanks guys for the help but we need more than 25 beds here. So let's take the 25 but how are we going to talk about not tens of beds but hundreds of beds which is what we're going to need," Dye said, without naming the donor in question.

Vigilante said the Liberian effort was switching to training community volunteers to staff local care centers, since "we cannot invent doctors and nurses overnight. "The American troops will certainly accelerate the availability of those beds but let's face it - the virus is running faster than us for the time being."

By Tom Miles and Stephanie Nebehay

(Editing by Mark Heinrich)