The United States is the world's second-largest soybean exporter and is facing stiff competition in top market China from cheaper producers in South America such as Brazil and Argentina. More than half of the US soybean crop is expected to be shipped abroad this year.

Despite the slow start to exports, the US government is unlikely to reduce export projections when it releases its outlook for supply and demand on Dec. 12, analysts said, because of uncertainty about the size of the crop from the rival Latin American producers due to adverse weather.

If the crop there is smaller than expected, then US exporters would benefit through additional demand for their grain to plug any gap in supply from Argentina or Brazil.

"I think it has been a talking point for two to three months," said Bill Gentry, broker at Management Commodities in Lafayette, Indiana. "But I think it is too soon for them to make an educated adjustment."

Corn exports are also off to a slow start, and analysts say the US Agriculture Department's forecast for overseas demand for the grain may have also been too bullish.

The USDA, which will release its latest outlook for exports, has only lowered its forecast for soybean exports twice in the previous 20 December reports. They have lowered the corn export forecast eight times.

Corn and soybean exports are critical outlets for a surplus of grain that has clogged up country elevators and weighed on commodity prices amid year after year of bumper US harvests.

With the USDA's December report, market watchers shift their attention from the supply side to the demand side of the balance sheets as the harvest of the US corn and soybean crops, the country's two biggest agriculture exports, has been completed.

During the first three months of the marketing year that started in September, 839.7 million bushels of soybeans were inspected for export, according to USDA data. That accounts for 37.3 percent of the government's projected yearly total for soybean exports.

During the previous 10 years, exporters had typically moved 41.6 percent of forecast soybean shipments during the first quarter of the marketing year.

For corn, export inspections have totaled 309.2 million bushels, or just 16.1 percent of the yearly projection, during the first quarter of the marketing year. They have typically moved 23.2 percent of the export forecast by now.

That is the slowest start since at least 1996, the earliest year that Reuters data is available on exports.

Still, the USDA has been criticized in the past for underestimating exports, so was unlikely to make any changes yet, said Ted Seifried, chief ag market strategist for Zaner Group.

Final soybean exports have topped the government's December outlook 13 times in the past 20 years. Final corn exports have come in below the government's December forecast 12 times and above it 8 times in the past 20 years.