* SIR20 done at 145.50-146.00 cents/lb, lowest since 2008
* RSS3 done at $3.63/kg, weakest since at least January
* Tokyo futures near their weakest since January
By Lewa Pardomuan
SINGAPORE, May 30 (Reuters) - Indonesian rubber was traded at four-year lows this week after Tokyo futures tumbled on worries the debt crisis in Europe could curb demand for commodities, while falling Thai prices spurred buying interest from China, dealers said on Wednesday.
SIR20 was traded in a series of deals among trade houses at 145.50 to 146.00 U.S. cents a pound ($3.20 to $3.21 a kg) for July delivery late on Tuesday, with up to 300 tonnes changing hands FOB Belawan port in Sumatra.
"SIR20 was traded at 146 cents for July, but demand is weak these days," said a dealer in Indonesia's main growing island of Sumatra.
SIR20, the cheapest grade in Southeast Asia, struck a record at 262 cents a pound in February last year.
Tokyo rubber futures, which set the tone for physical prices in Asia, are trading near their lowest level since January as a deepening debt crisis in Europe raised concerns about the health of the global economy.
But the low physical prices could attract more buying from China, the world's largest consumer, and prevent prices of Thai grades in Southeast Asia from falling further.
Thai RSS3 grade, considered the benchmark for physical prices in Asia, changed hands at their lowest level since at least January, tracking declines on Tokyo futures.
"Buyers from China are still sparsely around," said a dealer in Singapore, who trades Thai rubber. "RSS3 FOB Bangkok was sold at $3.62 to $3.63 a kg last night."
China's total tyre output in 2012 is expected to grow nearly 6 percent on the year to 483 million pieces, fuelled by demand from the automobile and other sectors and despite a slowdown in the world's second-largest economy.
There were no reports of deals for Thai STR20 rubber, but the Malaysian variety, SMR20, was traded at $3.38 a kg.
While sporadic buying from China could stir up trade next week, the market is keeping an eye on Thailand's intervention programme to buy USS3, the raw material for RSS3, that currently is running significantly behind target.
Thailand has bought only a fraction of the 200,000 tonnes of rubber sheet it planned to purchase under a government intervention programme, failing to boost prices, government and industry officials said on Tuesday.
"The Thai intervention is for RSS3, and that's a niche grade. It's no use when the main tyre grades are TSR10 and TSR20," said a third dealer in Singapore.
The government had approved a 15 billion baht ($471 million) budget in January to buy rubber from farmers in a bid to push up unsmoked rubber sheet (USS3) prices to above 120 baht per kg. But prices have continued to fall with the current 100 baht per kg even lower than January's 115 baht.
($1=31.80 baht) (Editing by Himani Sarkar)