BUENOS AIRES, Jan 28 (Reuters) - Argentina's upcoming soy crop is expected at 46 million tonnes, the Buenos Aires Grains Exchange said on Thursday, citing dry, hot weather as its reason for shaving a preliminary estimate of 46.5 million tonnes.

The country is the world's top exporter of soymeal livestock feed used to fatten hogs and poultry from Europe to Southeast Asia. But this season Argentina's famously fertile Pampas farm belt has been stricken by months of unusually dry weather.

"Due to high temperatures and limited water supply in key farming regions, our soybean production estimate has been reduced to 46 million tonnes," the exchange said in a report.

Planting of Argentina's 2020/21 soy crop ended over the last week on a total estimated area of 17.2 million hectares, the exchange said. Soy harvesting starts in March and ends in May.

Argentina is also the No. 3 global corn exporter and the world's No. 7 wheat supplier.

"The weather situation in both Argentina and Brazil is stable, but it remains fragile. If soil moisture in the coming weeks does not match the growing needs of crops, yields could be impacted," according to a report this week by the Geoglam global agriculture monitoring service in conjunction with the exchange.

Argentina is feeling the effect of a mild episode of the La Nina climate phenomenon this season, which tends to bring dryness to the region. This is happening at a time of tight international stocks and high demand for grains and oilseeds.

"La Nina conditions began in August-September 2020 and are currently forecast to continue from January to March," according to the report.

In the outlook for February through April, there is "a fair probability" of rainfall being below-average across much of Argentina, it said.

"Other factors are bringing uncertainty in the corn and soybean markets, such as export policies in the case of Argentina, and logistical issues in both Argentina and Brazil."

Argentina has considered limiting corn and wheat exports as part of an effort to ensure ample domestic food supplies as the local economy gets battered by recession and high inflation. Consumer prices in the country rose by 4% in December alone.

Pushback from growers and exporters who say agricultural export caps stifle farm investment and production has so far stopped the government from limiting international grains shipments.

(Reporting by Hugh Bronstein and Maximilian Heath; Editing by David Gregorio and Cynthia Osterman)