* Spot soybeans hit a fresh 5-1/2 month high in overnight trade at $13.32-1/4 before retreating. * Market underpinned by uncertainty about the size of the South American soy crop. Brazil's No. 3 soy producing state of Rio Grande do Sul will harvest a crop of 7.1 million tonnes this season, down from the 8 million forecast previously, the state agriculture agency projected. * US dollar edged lower, typically a bullish signal for dollar-backed grains and oilseeds, but concern about the global economy, euro zone debt and the pace of growth in China hung over the soy market. * Traders adjusting positions ahead of USDA's monthly supply/demand report on Friday that is expected to show a decline in US 2011/12 soy ending stocks. * China's Heilongjiang province, the country's top corn and soy grower, aims to raise total grains output by 8 percent in 2012 and will expand its corn acreage by paring back on land for soy, a local agriculture official said. * Taiwan's Breakfast Soybean Procurement Association will issue an international tender to purchase 40,000 to 60,000 tonnes of US or Brazilian soybeans - trade. * Iran's state-owned animal feed group SLAL has issued an international tender to purchase 100,000 tonnes of corn and 100,000 tonnes of soymeal, European traders said.