* Homs province has been a major battleground
* Only 3 doctors said left in province
* WHO says 550,000 need humanitarian aid
GENEVA, Sept 11 (Reuters) - A team from the World Health Organization that visited Syria's Homs province last week found a humanitarian situation that is "grave and continues to deteriorate", with one in four residents in need of humanitarian aid, the WHO said on Tuesday.
Homs is a central province that has been a major battleground in the nearly 18-month-old uprising that has pitted rebels against government troops loyal to President Bashar al-Assad.
Half the province's public hospitals and three-quarters of its private hospitals are out of action and those that remain open are working at reduced capacity and are overwhelmed, Tarik Jasarevic, a WHO spokesman, told a news briefing in Geneva.
He said most doctors had left and that the largest hospital in Homs, with 350 beds, had been completely destroyed.
"It has been reported that there are only three surgeons left in the governorate (province)," he added.
Out of the province's population of 2.2 million, the WHO estimates that 550,000 need humanitarian aid. As well as healthcare, there is an urgent need for food, shelter, water, sanitation and education, Jasarevic said.
Before the anti-Assad revolt began, Syria produced 90 percent of its own medicines and drugs. But production has been hit by the fighting, a lack of raw materials, and by the impact of sanctions and higher fuel costs.
The WHO had previously said that 90 percent of Syria's pharmaceutical plants were located in rural Aleppo, Homs and Damascus provinces and have suffered substantial damage from the conflict.
The city of Homs was the focus of world concern in February and March and again in June, when opposition-held neighbourhoods endured weeks of government bombardments and sniper fire in which hundreds of people were killed.
"There are 150 schools hosting internally displaced persons. The shelters that have recently opened provide poor living conditions; there is no electricity and the water and sanitation conditions are not functioning properly. Refuse is piling up - and has not been collected for several weeks," Jasarevic said.
The fighting has disrupted access to water and sanitation, as well as monitoring of vaccinations, and there is a critical shortage of life-saving medicines and materials such as vaccines, insulin, oxygen, nitrogen, anaesthetics and intravenous fluid sets.
Most of the city's health workers live in the surrounding rural area and cannot get to work. Many health facilities are staffed by untrained volunteers.
The situation was getting even more urgent because of the approach of winter, he said.
The WHO plans to supply basic health and water testing kits to Homs city while the Syrian Arab Red Crescent will monitor water quality and stockpile medical supplies and water monitoring kits to prepare for a potential outbreak.
The WHO has also asked Syria's Health Ministry to prepare a vaccine distribution plan that will include Homs province.