UPDATE 1-Civil war ravages Syrian farm sector-UN

* Syria wheat, barley output halves in 2012 vs previous yrs-FAO

* Less than half of farmers able to fully harvest crops

* Vegetable, fruit, olive, livestock output also hit (Adds detail, quotes)

ROME, Jan 23 (Reuters) - Civil war in Syria has left its agriculture in tatters, halving wheat and barley output and wreaking massive destruction on infrastructure, the United Nations' food agency said on Wednesday.

Following an assessment mission in Syria from Jan. 18-22, the Food and Agriculture Organisation (FAO) said wheat and barley output had dropped below 2 million tonnes in 2012, halving from 4-4.5 million tonnes in normal years.

"The mission was struck by the plight of the Syrian people whose capacity to cope is dramatically eroded by 22 months of crisis," Dominique Burgeon, director of FAO's Emergency and Rehabilitation Division, said in a statement.

"Destruction of infrastructure in all sectors is massive and it is clear that the longer the conflict lasts, the longer it will take to rehabilitate it," he said.

Peaceful street demonstrations seeking democratic reform in March 2011 were met with a bloody military crackdown and escalated into an armed uprising aimed at toppling President Bashar al-Assad. More than 60,000 people have been killed and 2.5 million displaced over 22 months of conflict.

The U.N. mission, coordinated with both the Syrian government and the opposition and composed of emergency directors from seven U.N. humanitarian agencies, visited areas around Damascus as well as the governorates of Homs and Dar.

It found that only 45 percent of farmers were able to fully harvest their cereal crops, while 14 percent reported they could not harvest at all due to fear of violence and lack of fuel.

Vegetable, fruit and olive production has declined significantly, with the mission finding a 60 percent drop in vegetable output in Homs and a 40 percent drop in olive oil production in Daraa.

Farmers are struggling to access seeds and fertilisers and irrigation is scant due to destruction of canals and pumps, FAO said.

Movement of livestock to grazing areas has been disrupted and animal survival is at risk due to a lack of feed and veterinary drugs, with imports hampered by sanctions, it said. Poultry production had also been seriously hit.

About 10 million people, or 46 percent of Syria's population, live in rural areas, and 80 percent of those rely on agriculture for their livelihoods, FAO said. (Reporting By Catherine Hornby; editing by Barry Moody and Keiron Henderson)