* Vietnam's 2009/2010 coffee crop at 16.67 million bags
   * 2008/2009 coffee output seen at 16 million bags
   * Rains help cut production cost
    (Adds details, comments)
   By Ho Binh Minh
   HANOI, March 6 (Reuters) - Vietnam has revised its preliminary forecast of its next 2009/2010 coffee crop, saying output could rise 4.2 percent to around 1 million tonnes or 16.67 million bags, a senior industry official said on Friday.
   "The crop can produce around 1 million tonnes, provided all conditions are favourable and the figure can be 5 percent up or down," Vietnam Coffee Association Chairman Luong Van Tu said after an industry meeting in the Central Highlands coffee belt.

Last week Tu told Reuters the country was expected to reap a lower coffee output from its coming 2009/2010 harvest, possibly less than 16 million bags, after two good crops.
   Tu said industry officials meeting on Friday in Dalat, the capital of Lam Dong province, agreed the harvest ending in January produced around 16 million bags, about 10 percent below the previous 2007/2008 output. One bag contains 60 kg of beans.
   Vietnam's coffee crop year lasts between October and September, starting with a four-month harvest. The Southeast Asian country is the world's second-largest producer after Brazil and is the biggest producer of the robusta variety.
   Traders believe the Vietnam Coffee Association often underestimates production figures to boost prices.
   The International Coffee Organization estimated Vietnam's latest harvest to be 18-20 million bags, while the U.S. Department of Agriculture put the output at 19.5 million bags, similar to the median in a Reuters poll of traders in January.
   Tu said partial dryness and unseasonal rains during the harvesting time have affected the quality of beans, with the size shrinking and the number of black beans rising, which are both  defects leading to export rejections.
   Farmers have been watering coffee trees for the next harvest but with about 20 percent of Vietnam's coffee trees old, output could not change much, Tu said in a telephone interview.
   He said production in the Central Highlands, which account for about 80 percent of Vietnam's total output, has been stable, while part of the coffee plantations in the smaller producing province of Dong Nai had been lost to industrial zone developers.
   Two other industry officials who also joined the review meeting on Friday said coffee production in Vietnam had stabilised in terms of both output and acreage.
   Daklak, the country's largest coffee growing province, is seen turning out 400,000 tonnes a year, followed by Lam Dong with 300,000 tonnes and Gia Lai with 100,000 tonnes, Van Thanh Huy, chief executive of Daklak-based export firm Inexim, said.
   "Rains have been falling across the coffee region and helped ease part of farmers' difficulties," the second official said.
   Domestic prices have fallen about 37 percent since last March to around 24,000 dong ($1.41) per kg of robusta.
   The dry season has been peaking in the Central Highlands and unseasonal rains help cut growers' watering cost and also trigger blossoms. Farmers, now in the second phase of watering, need to do it three times before the rainy season arrives in late April or early May. ($1=16,973 dong) (Editing by John Ruwitch and Clarence Fernandez)