*Price rises set for Monday - official source
*Prices to rise by 400 yuan ($58.59) per tonne
*Third price change in 2009, and biggest at 6-7 percent (Adds Sinopec source)
By Chen Aizhu and Tom Miles
BEIJING, May 31 (Reuters) - China plans to raise retail diesel and gasoline prices by 6-7 percent from Monday, industry and official sources said on Sunday, relieving some pressure on refiners but adding to the burden on farmers and manufacturers.
An official familiar with the issue said China planned to raise prices from Monday. Another official, at state-owned refiner Sinopec in northeast China, said he had had notice of the rise, which would be 400 yuan ($58.59) per tonne.
A second Sinopec official, based in south China, said he had heard the same number.
"Yes, there is talk from Shanghai and Beijing that prices will rise by 400 yuan from tonight. We are told again to wait for the official notice," he told Reuters.
That figure, also cited by industry website CBI China, would mean a rise of about 6.1 percent on gasoline and 6.9 percent on diesel, potentially sapping demand for the two motor fuels, which China is already exporting in record or near-record volumes.
The rise would be the third and biggest change in pump prices this year, after they fell in January and rose in March, but may not be enough to satisfy Sinopec, whose chairman Su Shulin has said the company is making refining losses with crude oil prices above $60 per barrel.
U.S. crude has doubled to more than $66 since dipping below $33 in January, supporting Su's case for a fuel price rise.
CHALLENGE TO FARM INCOMES
Higher diesel prices could also eat into farm incomes just as the agricultural season gets into its stride and could erode some of the consumption which is supporting China's economic revival.
China last raised gasoline and diesel prices by 3-5 percent on March 25, but it cancelled a rise of 8-9 percent at the last moment on May 7 after the cabinet, or State Council, apparently decided not to proceed.
A 13 percent rise in jet fuel prices on May 19 reignited talk that gasoline and diesel would soon follow, and analysts said Beijing could be testing the waters before adjusting the more sensitive motor fuel rates.
Gordon Kwan, head of energy research at Mirae Asset Securities, said last week that prices needed to go up about 10 percent for a "reasonable" profit margin in refining, one of the guidelines laid out in China's price setting system.
Under the system introduced at the start of this year, fuel prices are meant to track global crude oil prices more closely than in the past.
That should mean more price changes at the pump than before, when refiners often complained -- and demanded subsidies -- because they were being forced to provide fuel at a huge loss.
The formula specified in the reform allows for fuel prices to go up or down when global crude oil prices move by more than 4 percent from a 22-day moving average.
The vague terms make exact predictions impossible, but a surge in U.S. crude over the last few months had fuelled widespread hoarding, as Chinese speculators bet on a price rise.
Chinese government researchers had said the small-scale stockpiling was disrupting distribution of fuel within the country, while traders said the hopes of a price rise would slash China's diesel exports. ($1=6.828 Yuan) (Reporting by Tom Miles and Chen Aizhu; Editing by Myra MacDonald)