Brokerage firm Detwiler Fenton on Wednesday predicted that sales of Microsoft’s (MSFT) Surface tablet may fall below 1 million units in the slate’s debut quarter. The firm estimated that Surface sales in the fourth quarter could be as low as 500,000 units, well below earlier estimates of between 1 million and 2 million units. Detwiler Fenton’s forecast may be premature, however. Speaking to CNET, Rhoda Alexander of IHS iSuppli said that Microsoft’s tablet may sell more than 1 million units in the December quarter. In fact, the analyst estimates Surface sales could reach as high as 1.3 million units. The Surface RT tablet was released on October 26th, so if its sales were to exceed a million units then the company’s first tablet would equal initial sales of Google’s (GOOG) Nexus 7, which were estimated to be around 500,000 units a month. It has also been reported, however, that Microsoft may have cut Surface orders in half following the tablet’s slow launch.