Chicago wheat futures are set for their biggest weekly decline in almost four months, giving up some of gains made in November, as ample world inventories and a lack of demand for U.S. supplies pressured the market. The most-active wheat contract on the CBOT is down 3.3% this week, the biggest loss since the week ending Aug. 16. The rally in wheat prices in the last two weeks was overdone as there is no shortage of wheat," said one Singapore-based grains trader. "Australian drought has been factored into the market and we will not know the fate of the U.S. crop anytime soon as it is going to be under the snow until March.The wheat market had gained nearly 8% in the last two weeks due to short-covering and lower production in Australia. Wheat export sales of 228,100 tonnes were the lowest since mid-June and also below a range of market forecasts.